As for master cylinders, early dual chamber CJ5 or early non power brake dual chamber Corvette might fit in the space there. I think I still have one of those CJ ones somewhere. When using a newer MC drum brake type, remember to remove the 10 pound valve in the port you use for the front wheels, and plumb in a 2 pound if not your calipers may drag. see link here for good info: http://www.earlycj5.com/technical/brakes/early-cj-disk-brake-swap/
exerpt:
"Remember that if you are using a dual master cylinder from a drum-brake vehicle, you will need to remove the 10-lb. residual-pressure valve from the front port of the MC and plumb a 2-lb. unit inline to the front brakes I used a Wilwood PN: 260-1874. (The photo at left is from my incomplete installation). If you don’t remove that 10-lb. pressure valve, the front brakes will drag, as there is no spring to return the calipers like there is in a drum installation. If you just remove the stock valve and don’t install a 2-lb. valve like I did, you may end up having to double-pump the brakes all the time to get any pedal, as there is nothing to stop too much brake fluid from flowing back to the master cylinder when you release the pedal. Note the frame-mounted dual-chamber master cylinder from a 67-71 CJ-5. The purists may cringe; I just couldn’t bring myself to put a single-circuit system back into my CJ-2A when I was going this far with a “restification”. The old saying “no guts,no glory!” just doesn’t apply here I’m afraid.
Also, remember to install the calipers with the bleeder facing UP, so that it will bleed properly. If you reverse the calipers and have the bleeder facing toward the ground (a very common mistake) you will never get the system bled and your pedal feel will be horrible. Simply swap the calipers from side to side to correct this. DUH! Guess that’s why the calipers have different part numbers!"