Anybody running the '68 4 speed 340 cam?

Maybe I need to play with my timing. I do run the 68' 4 speed cam in my 69' 4 speed, with power brakes and the Vacuum is a little low for the booster to work well. I have no issue in my 72' Van with the DC auto transmission cam, with the brakes.
I have heard the vacuum is low for p. brakes. What number are you getting for vacuum?