Get a 200 r4 from a junkyard. Most of them have a multibolt pattern bell housing. You will need a new crossmember for that trans. Since it is a fresh rebuild, go get an Olds 350 and build it up while you can still drive a reliable car. Once you get the 350 done take out the 307 and drop in the 350. I am telling you to go Olds because every thing will swap over with no problems(all of the accessories, same motor mounts, maybe exhaust manifold????) I am pretty sure that you are able to use the computer equipment also, it should adjust for the bigger engine.