Driveshaft question

You existing trans mount should work fine although I
do not have much experience with spool mounts.
You will gain durability with the 727 but no performance
gain whatsoever, the 904 takes less HP to operated and cheap
2.75 planetary gears are available for it which help low to moderate
HP combos.ull

You will need to acquire a different converter, hopefully a 10 3/4 unit if
you are interested in performance.