Shift Kit for Early 904?

I plan to build the 273/904 combo going into my '64 Valiant soon. I am keeping the push-button shifter, but am not having any luck finding a valve body and/or shift kit to fit a pre'66 904. Are the differences in the newer transmissions such that i can't use those parts at all? Or can somebody point me in the right direction? I also plan to put a higher stall converter in - same issue with parts availability, although it seems a competent machine shop can machine one to work for me. Any other suggestions? I did a quick search of the forum, but the words "shift", "kit" and 904 are in here about eleventybillion times..

Thanks for any assistance!