When I set mine up with the Mallory kit the amount of advance was dead on when I checked it after putting the distributor back in.

Also, as you reduce the amount advance in the distributor you need to increase the stiffness of the springs to keep the advance all in at the same rpm. For Example: if you had 30 degrees of timing in the distributor and it was all in at 3000 rpm and you moved the stops to limit the advance to 15 degrees than it would be all in at 1500 rpm. When I did mine I used the orange springs which I believe are the next to stiffest to keep my 18 degrees coming in at 2500 rpm. The distributor came with the lightest pink springs.

Using a degree wheel would be awful inconvenient. They are so large in diameter it would be very hard to see what you are doing and trying accurately attach it to the end of the distributor shaft would be a chore. The protractor would be much easier.