Ok, I posted this question in the GM Truck discussion a few days ago but haven't gotten an answer yet...so figured I'd try posting my question here.

I'm looking at my options for upgrading my front brakes from drum to disk and I had a question regarding the booster. My truck is a 1970 Chevy CST/10 fleetside with power drum brakes. Since my truck already has power drum brakes, and has a booster, I was wondering if I need to replace the booster and why it had to be replaced. Or can I just replace the master cylinder and add a proportioning valve to the existing booster?

Any insight would be greatly appreciated. Thanks.
Brian