The only upgrades for drag racing would be a liberty gears faceplate and heat treatment job.
Not a do it at home kind of mod.
The factory service manual in as good as any as a reference
of the rebuild process.
Not sure what year transmission you have but the ball and
detent side cover has a better design than the later interlock levers for racing. Trimmed steel forks work well with the early
side cover.
Never run ATF for gear lube unless you like to rebuild often.
