Mustang Tech

have an early rebuilt 1970 fmx box it works fine up the gears hard or soft accel, kicks back fine when you stop at lights or a corner it just wont come back to 1st sometimes about 60% of it unless you go to neutral it has a trans go kit and 2500 stall all new parts where possible everything inside was goes was the report im thinking the gov if so what's the fix and how hard to get it out and do drain the oil

I'm not all that familiar with the FMX, but usually removal of the governor would mean tail housing off. You'd probably have to drain some of the fluid depending on the level.
The governors would normally have a removable mesh filter in them. They're pretty easy to pull apart and clean if it's sticking.