I had installed 742 gears in my 741 case. It was done in 1991, no issues through 2 trashed tranny's, 3 engines. Best guesstimate of max HP any engine in the car is 450+ HP. Gears are 4.10's.
I did the same thing,just used the bearing and races for the 742 case.My car went 10.40s with it and never broke.I got a dana cheap and put it in.There was no differance in times. Mark