3.2". Ford and Dodge are 3.2". GM is 3.4". How does a person remember such obscure differences? I always remembered there were 3.4" and 3.2" dimensions and I knew Ford and Dodge were the same and GM was the other but couldn't keep them straight. Since '32 Fords are popular and I can always remember that, I always think of '32 Fords and the 3.2" dimension when remembering the Ford hydroboost bolt spacing dimension.
I also have similar mind tricks to remember feed/return line placing on certain automatic transmissions etc. We old guys have to do stuff like this so we have a prayer of remembering anything

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Hope that helps.
Todd Z.