Rebuilding would be your easiest and probably cheapest option. Next option would be to whack a 2L in there, commonly called the pinto, found in your everyday Seirra, pretty much straight swap, although exhaust and intake are on the opposite sides to your crossflow, so theres a few extra things you have to do like rerouting the exhuast etc. Nothing tooo major. 4AGE would go real well, and theres alot of parts/bolt on upgrades available, although I've never seen this conversion done in the flesh I imagine it wouldn't be too hard