I have done both the 700 R4 and the Tremec 5 Speed. The 700 Needs the Crossmember Modified or replaced.  When I did mine the 82 Dipstick was still avalable. The Driveline Needs to be Shorten't too. The Stock Shifter will work to if You don't care about shifting into 1st I never found a Need. A company called Bowtie Overdrives can provide You with everything.  When switching to a Manual Trans its a a Bit More Complicated. You Will Need to Weld the Mount on the Frame that the Clutch Linkage Uses. Check You Block to make sure You have the Mounting Hole for the Other Side of the Linkage. Then You will have to Change Out the Clutch Brake Peddel Assembly and this is no easy Task You Might want to consider changing the Power Brake Booster at the same time if its Old. Now Your Ready to just Bolt in the Trans of Your Choise I'd go with the Tremec 5 Speed. The Tremec 6 Speed Weighs 30 Lbs more and the Trans Tunnel Has to be Cut to fit it. If You have a  Bit of a Cam in Your Engine You Might Find that Your Car Can't Pull 6th Gear down the Freeway when Your all done anyway. It will also take Driveline, Crossmember and Shifter Mods. Keisler and  Chevy 5 Speeds Sells Kits and or Parts to do them. Richard....