converter change

I was wanting to find out if a \6 converter fit in a v8 904, The \6 is a 63 and the v8 is a 66 904 or do they have different spline's.It act like it will work but won't slide all the way back. I have a newer model 904 out of a \6 and it will go right in but the end that goes in the crank is to big.Thank's for any help.......