going back to manual disc brakes from power

Regarding master cylinder bore size, check the factory part manuals and FSMs- I don't trust ANY of the aftermarket listings anymore. They've homogenized their listings to the point of accuracy being a secondary consideration.
According to the FSM, the factory used the 1 1/32 master on manual systems, and the 15/16 master on power systems from '73-'75 with the 2.6" diameter caliper piston.
In '76 they went to a 2.75" caliper piston and used a 1 1/32 master on both power and manual, IIRC- but I don't have the '76 FSM to confirm my memory on the master size.