your driveshaft may have a slip yoke built into it, but what is the transmission output. B&T or splined slip yoke?
read the post by @Professor Fate there is not such thing as 64~66 the break downs are 64~65, 66~67, 68+
if your transmission is 68+ you *might* be able to do some parts swapping. if it's B&T then you're SOL and would need to swap the main and tail shaft for sure, if it's even possible.