transmission interchangability ??s

I am wondering if the tail sections and output shafts of early and later 904s are interchangable? I am rebuilding my 65 904 and would like to switch to a slipyoke. I was thinking that if they were, that would be a good way to do it, since it will be out of the car anyway. Then I could just use a later model drive shaft, instead of cutting my existing ball and trunion shaft and adding a slip yoke to it. Thanks in advance for any ideas or info on this matter.