I bought a chinese knock-off Toyota 3k from Amazon for $50 and then bought a conversion kit off Ebay for another $120. Only a slight performance improvement but it idles super smooth now that the vacuum hoses a 99% removed. Starts much easier with the manual choke, too. Mileage didn't suffer a bit, but then, it didn't improve either. I get about 17-18 in town, about 20mpg on long highway stretches.
What precisely is in the "conversion kit" cos I've got a Chinese 3k knock off too and it bolted straight on and all I did was add studs from a 4k manifold and a Toyota carb spacer I did make a bracket for my throttle cable tho
I bought my 3k Toyota from Amazon for about $50 shipped. Didn't need to do anything to it prior to installation. Once installed, I used my vacuum gauge to set the idle mixture, then set the idle with my trusty Sears engine analyzer (from the 80s). Fast and easy install.
As for the ebay manifold kit, the seller included a choke cable and poly intake spacer that is cut exactly to the 3k carb. The bores are a little bigger and beveled. Without it, you'd have to modify your original spacer to make it work. He also includes the correct threaded fuel inlet adapter with nipple that he machines himself because this part doesn't exist in parts stores. There is 2 tygon fuel lines. One goes from the carb to the fuel pump, and the other goes to the vacuum port on the distributor. He includes a machined EGR block off plate and air cleaner adapter so that you can run your factory air cleaner assembly. If I didn't live in cold climates, I wouldn't worry about this but I wanted to keep the warm air pickup from the exhaust manifold. Lastly, he also includes all the rubber caps you need to block off the unused vacuum lines on the manifold.
Not gonna lie. The install was very straight forward and simple. Took longer to remove the stock junk than to convert to the 3k. What I noticed first was how much smoother the engine ran without all the vacuum leaks. Warm and cold starts are quick without all the cranking. Sometimes the fuel will evaporate out of the bowl on a warm day, so I just keep my foot on the throttle and it fires up, again, without all the cranking and building of fuel pressure again. The old Hitachi carb was always losing fuel pressure on me. Lastly, I didn't notice any differences in MPG or power. Was hoping to gain a little of both, but I didn't. If nothing else, its much cleaner under the hood and easier to tune. Plus, I'm getting ready to add a AMR500 supercharger (draw-thru) and there is no way I'd do that with the old Hitachi. Hope all this helps you with whatever decisions you're making.