Why not make it easy and install a small block Ford, with 4 speed auto behind it. or a vortec 350 and a 4 speed auto behind it. Parts are plentiful and reasonably priced. Shorty headers are avail for both engines, as are FI changeover harnesses.

Make some mounts, weld a driveshaft, custom some pipes and such... Bam a 300+ HP engine under the hood (granted it might be some heavier).