MASTER CYLINDER QUESTION

Actually, you are correct — they didn't use the 15/16 MC for power discs until 1973 — I just looked it up. Through 72 they were all 1-1/32. I wouldn't change the MC bore on a power brake system — you don't know what effect that would have on the booster (for example, what is the effect of a greater range of travel?). And since the brakes are already boosted, I can't see why you would want less pedal effort. It might be a consideration if you were thinking about converting to manual brakes.