Did you bench bleed the master cylinder BEFORE installing it in the truck?
Do you have residual valves in line from the master cylinder?
You may have them installed backward, that's why you aren't getting any fluid thru.
Remove the residual valves and see if the fluid will come thru the bleeders. To determine if your push rod is the wrong length. Try this:
(1)disconnect the push rod from your brake pedal and from the master cylinder.(2) Open the driver side front wheel cylinder bleeder. (3) use a screwdriver to push in the piston on the master cylinder. (4)Look to see if any fluid comes out of the bleeder as you push in the piston on the master cylinder.
You have the correct master cylinder Napa# M1974, '76 Corvette, 1.125" bore. Push rod clearance of 1/16" is OK.
