With 4 inch crank...i would use the standard gearing in the 904...
the 904 is approximately 35 lbs lighter with most that being internally rotating parts...
I switched from 727 to 904 back in 1993...the car picked up a good tenth and half...and the 904 converter was not as good as the 727....a properly build 904 will take a licking and keep on ticking...
all 3 cars in the signature below are 904s...and they are so simple to rebuild I do them myself...
