I used a stock manual drum pushrod with a cast iron 7/8 bore MC. Worked fine. Make sure you have some sort of retainer to hold the pushrod in the MC. The typical one is the small rubber sleeve. There is anot her style (older) that is retained with screws.
If if was me, I'd get a MC for a 73-75 power brake A body car but run it manually. BTDT and they're cheap.
I guess the big question is will the stock manual push rod work ok in those smaller 15/16 bore with a new rubber retaining ring? Just double checking the real world application out there. You know, check, check again and spend the $$$$ once.
