Manifold Vacuum Advance what am I not getting?

After you set the Tslot to square count the number of turns it takes to get it to idle (if necessary) and write it down .
But double check your balancer for correct TDC first . Can’t imagine your engine will crank over @ 40+ degrees intial. But you might have a dizzy out of a C-body or such with a 28*ish vacuum advance in it .

You know you can adjust when your vacuum advance starts by using an allen wrench ? You could max it out to see where your static timing really is .