I have a 2 bolt aluminum master cylinder I bought from
Rick Eherenberg many years ago I'm going to use. It has a 9/16" thread in the front port and 1/2" threads in the rear port. Which reservoir is front brakes and which is rear. I don't see much difference in reservoir size. Thank you for the help.

Front is rear and rear is front.

Depends. Typically, the rear port (towards the pushrod) is the higher volume port. On a big rear tire car with big rear brakes and skinny fronts, you want the rears to do more work and would plumb the rears to the rear port. On a street car where the front brakes do 80% of the work, You want the fronts to get the higher volume.