Push rod adjustment on 71 K20

[Murphy IRE]

My brakes still don't stop the truck like they should. So after all the other things that I've replaced and done, I' ve learned that the adjustment on the push rod is critical. Rememering that the PO said he "Just put a new Master Cylinder in" before I bought it. The pedal is not soft or spongy, it has normal feel. If I stand on the pedal the truck will stop, but I can't do an emergency stop.
So, Do I need to remove the master cylinder to get at the push rod? Also, how much should I adjust it? I've attached a pic (It's a Delco MC). Any and all pointers are greatly appreceiated, Thanks in Advance!