I converted by 4 wheel drum manual brake car to power discs about 15 years ago. When bleeding my rear brakes, a member in the audience noted that the rear compartment on the master cylinder was using fluid. He said the front compartment is for the rear brakes. Have I mixed up my lines?

Most GM cars/trucks are front res./front brakes rear res./rear brakes setups, yours is correct. Chrysler uses front res./rear brakes rear res./front brakes on a lot of vehicles, not sure about Ford.

The larger reservoir is for the front brakes if there is a size difference.