If you could get a drop out, that would be easiest. You may be able to use one from a Grand Prix, but i am not certain on that. They are all w-bodies. You'* have to get a wiring harness from a 98 (unfortunately I tossed my spare one a while back) and mod it if you got an L67.
If the transmission is the same as a Grand prix one, you might be able to get the PCM from that year Grand prix and make it work.
Just thinking out loud on a lot of this and it'* not tested, but should work in theory.
2007 Saturn Aura XR | 1970 Chevy Blazer 4x4 | 1970 GMC 3/4 Suburban 4x4