727 trans question in 383 A body

hey guys- I am collecting parts to put my 383 in a recently aquired 69 Valiant. Is there a "correct" 727 tailshaft for the big block swap. Will the car retain the /6 crossmember. I am good on the 8-3/4 already. Secondly, does anyone know of internal differences (heavy duty) on the motorhome 727's other than the tailshaft being different? thanks for the inputs.
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