I made the switch back in 1993,,,

removed a 727 with a turbo action 4400xxsm converter which was set up for the car.

and put in 3800 series converter with a 904 which was probably a little too tight for the car.

i did pick up approximately .15 and 2 mph.

Tony

70 AARCuda Vitamin C
71 Dart Swinger 360 10.318 @ 128.22(10-04-14 Bakersfield)
71 Demon 360 10.666 @122.41 (01-29-17 @ Las Vegas)
71 Duster 408 (10.29 @ 127.86 3/16/19 Las Vegas)