727 -> 904

I have the possibility to buy a ´79 A-904 with TCI pan and TCI 2600(?) stall converter. Bands and clutches are worn, as I was told its driveable but would rev when braking. I´d go through the internals anyway...
I think about installing it instead of my badly leaking 727. Car is a ´68 340 Cuda with 8 3/4 rear.
What would be the mayor issues in the swap? Can the driveshaft be lengthened or woukd i have to buy a new one? What about crossmember and linkage?

Greetings from hot Bavaria