My Dart that I converted to a big block/727 was originally a slant 6 with a 904. Can I use the transmission crossmember and biscuit type mount from the 904 on the 727? I would get a new biscuit if I can. Also, I was wondering if I should switch to the later spool mount type crossmember. Is there any advantage to using a spool type mount or will I be O.K. with the biscuit mount crossmember I have?

Auto trans crossmember is the same 727, 904.

Converting to the spool xmember will making seeking the rubber mount a little easier in the future , from what I hear the biscuit mounts may be slightly taller than original ?

i bought a replacement mount for my 69 charger, and it appears it may be slightly taller, but i haven't installed it yet.
as the mount there now is the original, it may have shrunk or slightly settled/collapsed since new, 55 years ago.