Master Power Brakes sell new reproductions of the desirable late model A body spindles. They'll also sell you a stock style complete kit made to work with 14" wheels.

My choice was a 13" Baer system with the late model spindles and 17" wheels. It works well - I can stop at speed with confidence. I do need to get a dual diaphram booster however to get full benefit; a project for this winter.