Where do i start... I started with a 77 non locker. After finding it had 3 pinion planetary from and rear I pulled the 2.74 low gear and 4 pinion planetaries from a 79 lock up. Drilled 1 1/4 holes in the sun shell to lighten it. Removed the governor and dead weight on the output shaft. New stock...
If you're curious about 904 tricks I know a few. I have a 511 BB bolted to my 904 with the JW Ultra Bell. 752hp and 658ftlbs in my 3077b Laser. Full season on it and its still shifting great.