Are these going to be be power disc brakes? I'm not going to be able to help with your specific application, but here is some info. The rod length will give or take away mechanical leverage. When my instructor put power brakes on his Nova, he left the rod in the same location as non-power brakes. His brake pedal arm had two holes drilled in it. A lower one for manual brakes, and a top on for power brakes. Anyway, he hooked it all up and went for a test drive. If you even thought about touching the brake pedal the car would screech to a stop. Power brakes won't require all of the mechanical leverage that manual brakes do. You might have to try it out and fine tune it from there. Sorry, I can't help more. John.

1968 Chevy C-10, 250 and 3 speed on floor, Hedman headers, Offy intake, Edelbrock 600cfm 4 barrel, HEI
1966 Chevy C-10, motor and tranny went into the '68. Waiting to be restored.