Hey Bram - LS1 or 2s, doesn't much matter if you can attain your performance goals and within budget. Heck, a 5.3 can be found here for $500 and with heads and a cam can make 475 fwhp! LS1s are considered Gen 3 and LS2s Gen 4 architecture. Both are well supported by the aftermarket.
A good place to start is the stickies on PT:
http://www.pro-touring.com/forumdisp...-The-LSX-Forum
Also poke around on LS1tech.com. There's great info there! My personal choice would be a LS2 for the cubes with a throw some L92 heads and a cam and see 500hp+ all day long.
One thing to add to Rybar's comment is fuel system mods. There's lots of options there as well!
