First off, the spline is 26/24 on 70 or 71 and later and 24/24 on pre-70's, as I understand it. There was one year that used 26/26 input shaft. It would possibly require changing some internal parts in the transmission to accept the shaft or it might not. Try and see if the 26 sline shaft will work. You will also have to change to the larger diameter flexplate (flywheel as some like to call it).Second question, yes, you can exchange the bellhousing provided...1) the cases are the same....or 2) the large bellhousing bolts to the pump not the case.
If the larger bellhousing bolts to the case and the transmission you are wanting to use has a bellhousing bolted to the pump, you have to search for another bellhousing like mentioned in #2 above.
My .02, find a later model C4 with bell and have it rebuilt instead of mixing and matching.
[This message has been edited by Just Strokin (edited 04-19-2002).]