Master Cylinder question.

I think the M1627 that doesnt have the piston retainer is made for manual brakes. The brake rod and pedal hold the piston in while the power brake booster setup needs a hard stop for the piston. Im getting one (Fenco, ordering one today) from Autozone, 20 bucks with a 5 core, Im just going to give them my drum/drum symetrical MC as the core unless there is value here on the board...