Here is what I ended up doing.
1965 GMC drum/drum
Power booster CARDONE 503715, 67-70 C10 application
Cut the eye off the end of the rod, threaded it 3/8”, 16 NC
Used a locknut, with a threaded 1.75” long union on the pushrod, drilled the union and rod, cotter pin.
Shortened pushrod length to 4.25”
Threaded the end which bolts up to brake pedal longer.
