10" or 11" Rear Drum Brakes?

I am switching my Duster over to use large bolt pattern (lbp) wheels from the small bolt pattern (sbp).

I am going to keep the Kelsey Hayes front disc brakes but use the Mustang rotors for the bolt pattern.

My question switching the rear brakes...should I go with the 10" or 11" b-body drum brakes?

Or does size really matter?

How is parts availability for both?

Thanks in advance.
Paul