The question was about a dual reservoir master cylinder rather than a power booster although a lot of our members would be interested in that topic as well.
Concerning a dual reservoir master cylinder, you may not realize it but the original 51-55 Kaiser MC is part of the brake pedal linkage in that the brake pedal arm pivots on a brass bushing in the MC casting. (That's why you need to look closely at a replacement MC unit to see if it comes with the bushing). If you want a dual reservoir MC, not only will you have to figure how to mount it, but how to pivot the brake pedal arm. Once you figure that out, arranging a way to fill the MC and re-plumbing at least 60% of the brake lines would be small challenges.
So you think you can avoid this by altering the car to a firewall mounted MC? That may be only switching all your problems to an area you can get to easier.