Howdy crowsgmc,
A while back I asked many of the same questions and folks were kind enough to give me the benefit of their experience, so let me pass some of it along.
1. No, the 'Vette master is not required. There are lots of options, but you do want one for a drum/drum system. A '67 or '68
drum/drum Belair master will work fine.
2. According to Master Power Brakes, no proportioning valve is needed with drum/drum dual brakes.
3. I can't answer this one, I didn't use one, but a booster only "boosts" input pressure. Your brakes will only be as good as your shoes and drums.
4. No, the larger the bore of the master, the harder the pedal will feel. Again from MPB. Stick with no more than 1 1/8." I used a 1" bore master from Sachse Rod shop.
5. Oh, yes! As I understand it, you have to change your clutch pedal,too. That means more expense and hassle. The under floor
bracket is available from many outlets from about $55 up.
My conclusions run like this, to improve braking, you must improve your brakes. This means discs. I didn't want to go that route, so the dual master is for safety. Nothing else that you could do will change anything but "feel," as long as the rest of the system is in top notch shape.
You will also have to "replumb" the brake lines. Not a bad idea anyway on old trucks like ours. There is an excellent article on doing this in the "tech tips" section of stovebolt.com
Best wishes,I hope this is what you are looking for.
