Bullet proof A833?

I have a 67 Dart , pretty built 340 with a 4 speed. I'm looking to build a "bullet proof" A833 for it. I blew 3rd gear power shifting on the street (Damn you RAM paddle disc) and I replaced the tranny with a stock A833. I've been taking it easy as far as power shifting and dumping the clutch etc. because i don't want to grenade this one too. The transmission has an aluminum tail so I'm looking to build the internals so I don't have to worry. Any ideas of which gears etc.? Thanks in advance.