What transmission will fit A 1963 Oldsmobile dynamic 88?

Trying to install any transmission other than the original (Rotohydramatic Model 10) involves a lot of work. Newer Turbo-Hydramatics (TH400, TH350, TH200-4R, TH700-R4) do not bolt up to the engine flex plate or bell housing, the drive shaft yoke will not fit, and the drive tunnel (hump in the floorpan) will need to be cut up and enlarged to fit these newer (and larger) transmissions. The original transmission for this car was known as the "slim jim" for good reason. It was unsually long and very narrow in cross-section - to allow a smaller drive tunnel and more footroom up front. Trying to squeeze a newer transmission under the car without contact with the floorpan doesn't work so well. There have been a few home mechanics who "made some room" by taking a sledge hammer to the floorpan to create enough clearance for the 200-4R trans. The adapters for the 394V8, the custom mangling of the crossmember and mount, and driveshaft all make it a frustrating (and expensive) project for the novice.