To bad you gave up on the hydro boost. Hydro boost is a great solution. My brakes in a Challenger = Hydroboost, 11.75 dia stock slider calipers front, Ford calipers out back, 4 wheel disk GM prop valve (straight thru). Rear parking brake hooked up or not, either way. Easily skids the tires. And that's with a large bore master cylinder.

I should check the psi at the calipers with hydro boost now. Never did because it solved the problem. I'm sure its way more than 1200. When I checked my manual brakes setup with 7/8 bore it was 700 psi. When i switched back to stock power booster (single but large diameter), engine vacuum was 14 and the psi was 1200 at front caliper.

My opinion about stock booster is you need to get the vacuum up near 19-20 to get impressive brake performance.