Here are my thoughts on the Suzuki 2.5L to 2.7L swap, more or less in the order of assembly:
1. Select the engine.
Mine is a 2004 Suzuki XL-7 engine, I can confirm it works well. Earlier years H27a should swap over but I wouldn't use the later years' engines before doing the research. I can't confirm compatibility of any other years.
2. Get a factory service manual.
The Suzuki service manual on this forum is a great resource. I have my own GM factory manual. I've used both. Either one is suitable, and they are invaluable for torque specs and etc.
3. The Approach.
Generally you will be using the 2.7L short block and attaching all of the peripherals from the 2.5L, except as explained below. (I'll skip the details of your typical engine installation.)
4. Engine prep.
Strip the alternator and bracket, PS pump and bracket, fuel rails, injectors and harness, AC compressor and bracket, plenum, intake, throttle body, front coolant pipes and all connectors from both engines. The first obvious difference you'll see is that the 2.7L engine has a butterfly valve located on the front crossover air chamber. This affects the position of one of the flanges on the front crossover chamber which is therefore NOT interchangeable with the 2.5L intake. The 2.5L engine has no butterfly valve at all. I considered trying to use this valve for performance reasons but did not, for reasons explained in another post on this forum.
IF YOUR VEHICLE DOESN'T HAVE A KNOCK SENSOR, strip the knock sensor from the 2.7L engine and replace it with a short 14mm bolt (use teflon tape). My 2002 Chevy Tracker's wiring harness does not have a connector for the knock sensor. (If your original 2.5L Tracker or GV engine had a knock sensor, you may need to rethink this. )
Pull the timing cover and do a complete service as you would for any engine swap, with new gaskets, o rings, sensors, etc. The parts stores list separate intake gasket kits for the 2.5L v. the 2.7L, probably due to the butterfly valve. I used the 2.5L kit and had no issues. The water pump, o rings, gaskets, timing tensioners and guides were all interchangeable (however I didn't do a complete timing service - just the service recommended in the Suzuki TSB on this subject).
The camshaft position sensors (CPS) on both engines are located on the top rear of the L head (bank 2). After CAREFULLY marking the location of the original 2.7L sensor with a grease pencil or marker, remove both sensors but leave the bracket. The earlier model (USA) CPS will have a black cover. The updated CPS will have a bronze colored cover. Use the black one! The 2.5L computer will not comm with the 2.7L CPS.
Reinstall the 2.5L sensor on the 2.7L head while the engine is still on the stand, using the reference marks previously mentioned. I wasn't careful here and had to use the grease marks from the torx screw on the original 2.7L CPS to line up the replacement.
The thermostat housing itself appears to be interchangeable but one or more of the coolant necks is not. Use all cooling components from the 2.5L engine.
For AT vehicles, the flex plate is interchangeable. Here I also replaced my rear main seal which is also interchangeable. I don't have any additional info on the interchange as between manual transmission vehicles, but I'm guessing it is the same.
The timing cover, seal and CMP sensor are all interchangeable.
5. Installation.
On removal I pulled the left CV axle, exhaust manifolds and front differential, for ease of access. Re-installation is typical. Note the XL-7 wiring harness has a knock sensor wire / connector, located with the group of O2 sensor connectors at the center rear of the engine. Five connectors total in this 2.7L group. You probably won't find this knock sensor connector on your (USA) 2.5L wiring harness. There are only four O2 sensor connectors at this location, on a 02 Tracker ZR2 anyway.
Use the PCM (ECU) from the 2.5L. Except as mentioned, all connectors are compatible.
The XL-7 was fitted with a larger alternator than the Tracker / GV. I believe the 2.7L alternator is rated at about 90A, while the 2.5L alternator is about 60A. The larger 2.7L alternator will bolt right up, and all three connectors are interchangeable. The upper and lower alternator brackets on the 2.7L do have minor differences from the 2.5L brackets, but they are interchangeable. I used the larger alternator of course.
Use the injectors, injector harness and fuel rail from the 2.5L engine. Clean and pre-assemble your intake manifold. The 2.7L injectors are white, and the 2.5L injectors are green. I didn't attempt to use the white 2.7L injectors because it appeared the pintle diameter was different and therefore might not fit the 2.5L intake manifold. Use the green ones in your preassembly.
Use the engine mount brackets from the 2.5L engine. Apparently the 2.7L engine mounts are not interchangeable onto the 2.5L body. I didn't ask questions here, so I don't know for sure. I used the original brackets from the Tracker and everything bolted up fine.
Pay close attention to the AC compressor bracket setup. As I explained in an earlier post, the 2.7L AC bracket has four long studs to affix the compressor, while the 2.5L bracket uses two studs and a bolt (or three bolts in my case - it changes in later model years). There are also some small spacers in some of the 2.5L AC brackets, which will affect belt length if you mix up your 2.7L v early 2.5L v late 2.5L AC bracket parts. Just use the original equipment from the 2.5L air conditioning setup. All of it.
The PS pump, reservoir and brackets are all interchangeable.
I used the serpentine belt and alternator belt spec'd for the 2.5L engine. The 2.7L belts are probably interchangeable, but I wasn't sure, given the incompatibility of some AC components. My 2.5L serpentine belt is tight but seems to fit just fine.
Exhaust reassembly is typical. I used a combination of 2.5L and 2.7L manifolds which were interchangeable. They bolt right up to the exhaust ports and the gaskets are identical. There is some suggestion the 2.5L exhaust is too restrictive for the 2.7L. I will probably replace the muffler with a less restrictive resonator when I get a chance.
You should probably check the engine timing adjustment section of your service manual, tho I haven't done that, and I'm not sure I'll need to. The CPS sensor can only be installed one way into the receiver. In other words, you can't install it upside down, or 180 degrees off. However you'll need to rotate it EXACTLY to the position it was in when removed from its bracket, using your reference marks. Your timing should be pretty close to what it was when you last started your engine. However, follow the instructions in the manual for timing adjustment to be sure.
The 2.7L engine height seems to be identical. Use the original 2.5L throttle and TV cables and brackets.
The coolant inlet pipe on the 2.7L is NOT interchangeable. This means the coolant inlet hose is also not interchangeable. Use the entire 2.5L cooling system setup. The coolant pipe o rings are all interchangeable, as are the radiator and all other fittings.
That's pretty much it. I'll add photos later and edit this post if I think of any more details.