no sense messing around trying to get a bolt out on a wheel cylinder your not using; and if your rebuilding it your own your crazy, you can buy them cheaper
a lot if not most of "new" wheel cylinders nowadays at autozone, etc. are offshore knockoffs. asian, not north american. i try to use kits if at all available when doing rear brakes. have found old delco moraine cylinders in the yards that i have sold for $50 a pair to resto types.