Eric - I put a booster on my drum/drum brakes & it REALLY helps. At the same time time I put a double res. M/C. No prop valve is needed since both axles are drum, there's no need to proportion. I never even thought about resivoir size. Long as you fill it & it don't leak, anything should be OK. I did it all with wrecking yard parts & some mounts I welded up.
Doug
