If your running front disc/rear drum you probably don't want to use a corvette master ---Your best choice would be a master from an late 60/early seventy Ford product that was for front disc/rear drums--they probably will already have the residual valves built in and your only concern would be matching front brakes to the front fitting and rears to rear

I have seen your complain on a few Cobras with mismatched components--there is a little difference on the spread of the mounting holes but a little time with a rat tail file will fix that

Jerry