I've rebuilt about a dozen torque flites mostly being stock rebuilds and shift kits
I'm about to build a 904 with a transbrake, what mods can I do or need to do to the internals of the Trans for the brake?

There are lots of posts about this but I'll throw these out there.
Front drum w/ 5 dics Scarf cut sealing rings w/ stock drum chrome w/ alum drum
Multi pak front clutch springs
Top quality bands & clutches red? I don't remember my clearance but I'm thinking .008-.010 per disc
move the vent to the rear
Needle bearing output shaft support
If your over about 650 hp billet input & output shafts
Lots of line pressure 175 is what mine is and its maxed out w/ a HD spring,
There's more but this is a start
Several moparts sponsors can supply what you need. A&A TCS protrans

Should have a trans brake converter which has a steel stator or this can happen. Change from slot drive to the a500 flat drive pump drive. Billet low rev & kick down servo. Wide kickdown band.

BTT