Get a stethoscope and locate the source of the noise - lifters will be up in the heads, chains/tensioners will be in front.
A repetitive tick is more likely to be a lifter, a continuous rattle (yes it will vary with engine speed) is more likely to be the chains, the tensioners themselves are unlikely to make any noise, because what they do is move the adjuster that keeps the chains tight.
There IS a bulletin (TSB No. TS 07 03014R2) documenting the tensioner issue with the XL-7, and this covers a rattle from the front of the engine at startup, not a continuous tick - you can call Suzuki back and ask them to check that number, but, that was up to 2002, I would expect your 2004 to already have the updated tensioner.
A couple of comments - and this is just my opinion - first - if the engine has been neglected, you're not are not going to find a "quick fix" in a can - there's no significant flow of oil (and therefore flush or additive) through either the lifters or the tensioners.
Second - do you really want to run an engine on a lighter oil that the manufacturer recommends - I feel oil "weight" should be determined by temperature, cooler climates, lighter oils, hotter climates, heavier oils, and always guided by the manufacturer's recommendations - of course, if you're an engineer, and know more than the manufacturer's engineering team...
98 - 1.8 Mitsubishi Pajero iO
98 - 2.0 Suzuki Grand Vitara - SQ420
05 - 2.0 Suzuki Grand Vitara - JB420