I am trying to put any basket case of a 1969 Old 442 back together but do not have a master cylinder or brake booster. The car has front disk and rear drums. Can anyone advise the proper size of booster i should be using.

 

The stock booster is 11". Correct replacement A-body boosters and master cylinders pretty much grow on trees, since Chevelle is the same. Be aware that if this is a FACTORY disc brake car (as opposed to a conversion), it does not use a proportioning valve or combination valve. Olds carefully selected the size of the rear wheel cylinders to achieve the required front/rear brake balance without a prop valve. There should be a metering valve under the master cylinder. This is NOT a proportioning valve and performs a completely different function.