Mopar Aluminum Master Cylinder Kit

Definitely 15/16.

My 68 has 73-75 front discs and 10x2-1/2 rear drums.
I have had 1-1/8, 1-1/32 and 7/8 bore MC's on this combination all run manually. I liked the 7/8 bore the best because it gave a nice, easy, linear feel.

Currently running a NOS Direct Connection 1-1/32 aluminum to save weight. It could be a little less hard for me but it's fine. A 15/16 should be perfect!