Master Cylinder Bore?

Another vote for 15/16"

Manual front K-H, rear drums. When I first swapped from a single pot on my 66 Barracuda, I put on a 1-1/16". The brakes never felt right. Several years later I put in a 15/16" totally happy with the brakes now.
Dig that! I should probably replace all the lines. They're original. You should have seen the original gas line at sending unit I pulled out of that damn thing look like you're staring down in the inside of a cave with stalagmites growing up horizontally out of the walls, in a mountain range. When I did the 66 Sat, I bought a tubing Bender, a double flaring tool (cheap ones) a 20$ roll.coil and bent em up myself. Sort of a pain in the butt it was rewarding I learned a few things like using your tubing cutter versus a mini cut off wheel on a Dremel makes a difference when you go to do your inverted flare. The tubing cutter " work hardens" the tube.. the main thing I learned though, even if you change them one at a time, like I did you, should probably keep bleeding the air out of the system as you go, because once you finally change all those lines, and they're all full of air, even if you gravity bleed the system, strange things happen, especially if the guy who sold you the car had somebody hang the calipers inverted. Took me a lot of research to figure out I had to cut a piece of wood to stick to them and then it pull them off and hang them upside down so the bleeder valve was oriented.blew a few wheel cylinders too..