42RH / A500 question

Either one will work. Your going to rebuild it anyway. Use the good stuff red lining clutches and bands. Billet Servo pistons and reinforced struts.
In the end it will be stout.
Get Hands Torqueflite book.

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This will help with the front rebuilding.
Take the od with the new parts for it to a tranny shop that can press it apart and rebuild it for you.