You shouldn't have any problem converting to a more modern dual chamber master cylinder. Oldsguy converted the brakes on his 69 Delta 88 from power assist to manual. I would think the only thing you would have to do is make sure the movement of the plunger in your master cylinder allowed full actuation of the slave cylinders. Moving the master cylinder would be a bit more difficult. You would actually have to change the geometry in how the brake pedal moves the plunger in the master cylinder. If you are good with engineering this would be easier.
PM Oldsguy or keep this near the top, he can at least let you know what it was like modifying the brakes on his Delta. Also, someone else might have already done what you are looking to do. Good luck!
