904 to 727 swap

Don't know about the kickdown linkage, but a 727 will fit as it came with 340's from the factory. Mount & crossmember are in the same location. Not sure if the cooler lines will be the proper length or can be "adjusted". But fitings are the same.

You said "tailshaft". I'm guessing you meant "driveshaft", which will need to be shorter with the appropriate slip spline yoke.