The best bang for the buck is quite simply the TII motor. They are in abundance, and they can make good power. To back up that good news, all you need to make one fit is the front engine cover off of a GSL-SE's 13B along with the oil pan. The ECU would be the complicated part of this task.
My personal approach is the 12A Turbo, using everything custom fabricated and going with a carbed 12A with a blow through turbo setup. It has been an extremely slow and long process, but she is getting there. Trust me, this setup will likely cost just as much as the TII swap, if not more, after all is said and done, but both engines can put out enough power to rock your world. Finding 12A parts in good shape are just too hard to do now, though. Go with the TII swap.
For this information I just require the 12A you'll be replacing.
