Positraction - '57 Special '66 425 swap

I want to apologize ahead of time if this question has already been asked but I'm currently rebuilding a '57 Special with a manual trans and mating it to a '66 425 (old 364 block cracked ) and to help it hook up I'd like to know if there is a bolt in "positraction" rear differential that would work.

In some of the early Chevy's I know that they were easily identifiable with the large "P" cast into it. Are these interchangeable or is there another option

Any help would be appreciated.