put my hydroboost and master cylinder from a 04 mustang in the 71 today.
had to fill in the old bolt holes on the mounting plat and drill new ones (easy). After remounting the plate i notice one of the holes was completely covered by the hydroboost unit it self. No room for the nut to go at all.
I shaved about half the head off the bolt then cut a sliver off a 2" alu. pipe to make a shim/washer/spacer to push the mounting bracket away from the hydroboost. First try this made room the bolt and a lock washer.
Everything fits nicely. No problems with alignment of the petal at all.
Sorry the pic is kinda crummy... ill work for more in better light.