Can you lock up your disc brakes?

Sounds like you built your own version of ABS.Have you measured the stopping distance at a said speed? Say 30 MPH ?
That would be my main concern. Check what a new car in similar weight stops at 30 MPH and do a test (yeah, all new cars have power brakes,but you get the Idea)I have SSBC manual 4 wheel discs on my 65 B body. It stops well and short without any lock up. I set my prop valve till the rears locked and then backed off 2 turns.Works for me.
I understand you have yours wide open. If you are pleased with the way it stops,sounds good to me.