1963 & 66 c 60 questions

[S250]

hello,

first of two questions, I have a 1963 gmc c 60. I want to upgrade the master cylinder/booster system. once that little thing is empty that's it and it does leak, I think into the booster? I don't know where else it goes, I rebuilt the entire brake system not long ago. Any ideas for something more modern or safer that doesn't take a lot to convert?
I also found a 1966 c 60 complete, I know I cant use a lot of the body parts, but my friend has a c10 or 20 66. besides the front fenders, would that even fit on there?? I was told it could but no one could tell me what it takes to do it besides a lot of work.
thank you