Swap 904 to 727?

I am new at this and haven't been a member long. This question has probably been ask before but I wasn't on here to see it. I have a 66 Dart Gt.Changing from a 225 Slant with a 904 behind it to a 78 318 with 727 behind it. I do not have the 727 crossmember. Can I use the 904 crossmember? Having a problem finding one for the 727.