low powered trail machine, 2.0L tracker.
moderate power making a big difference in all around ability, 2.5 or 2.7L tracker/GV/XL7 engine and trans, turbo ecotec out of a solstice or cobalt ss, 3400 out of grand ams and similar. A 4.3L would probably be the last on "my" list but it is a common swap in the sami's. Run a good 3 or 4 speed auto trans to a dana 300 and it'll make your K5 stay parked more often than not.
If I were doing another light-ish tracker build again it would probably be powered by something like a solstice GXP turbo ecotec to the factory 5L40 (i think that's what it's called) trans and then make an adapter to a dana 300. 300hp, light and compact.