[Excaliber]

Just disconnect the vac unit when you setting, adjusting and checking strictly the base plus the mechanical advance. THEN, after your done with that, plug in the vacuum unit. At that point, you can check it, observe it but it basically is what it is. Adjust your idle mechanical screws and carb air/fuel ratio idle screws last WITH the vacuum in place.

Vacuum advance with an MSD add's about 10-15 degrees or so, IF the unit does get the full vacuum signal. Actually that's not common under cruise conditions and impossible under any kind of throttle application when vacuum falls very low. So, under theoritcal ideal unlikely conditions your total would be:
10 plus 28 plus 15 (highest possible) = 53

Generally speaking 50 is about the max to shoot for, 53 is a tad high, but it's doubtful you will even see 50 under cruise conditions. Maybe under decelleration conditions when total timing doesn't really matter anyway.

I run 30 BASE timing and another 10 MSD mechanical advance. I use a custom CNC made limiter to stop the MSD mechanical advance at 10 degrees. I think the best MSD provides is an 18 degree limiter (black), to much for me, so I went after market.

My motor cranks fine with a stock OEM Ford starter even when the motor is really hot, like right after a couple of hard laps at the track.