DJ,
I've played around with trying to put a 700R4 in my TH350's place, and I've found that it's more of a hassle than it's worth. First off, you have to consider that if you're going to get a 700R4 you need to make sure that it's newer than (I believe) 86. The 82's to (I believe) 86 were one of GM greatest nightmares, due to the pumps breaking. GM redesigned the 700R4 in (Again, I believe) 87. Okay, so now with that said, you still want to put in a 700R4.
Yes you will have to redo your driveshaft, by how much I don't know (I'm giving you my experiences with a TH350 in my Vette. I also have a 69 Malibu). You will probably also have to modify your crossmember too. Keep in mind that the 700R4 had different tailhousings, depending on the model it was put in. I bought a 700R4 out of a 93 Firebird and tried to swap it into a friend's 82 Crossfire Injection Vette (which also had a 700R4). Imagine the surprise to find out that not only did I have to swap out the tailhousing, but I also had to swap out the valvebody, because in the early 80's the Vettes had a 4 prong electrical connector, and the 93 had a five prong connector (I don't like screwing with changing the electrical wires). It turned into a pain in the rear, but I did get it to work. Now I have a broken 82 700R4 with a 93 Firebird valve body and tailhousing. If you want to save yourself a headache, I have heard that there are aftermarket overdrives for the TH350. Supposedly it's incorporated into the tailhousing unit, and supposedly it ain't as great as the new 700R4. I am still checking into this. If anyone knows anything about a website where this can be confirmed, please relay it. I hoped this useless trivia helped you out a little DJ.
Stingray L82
[This message has been edited by StingrayL82 (edited 11-20-98).]