Vacuum advance pod

I think all his work only got him 24 degrees. I'm guessing that's all that is possible,lol.
If you put a vacuum pump on the nipple and evacuate the chamber while watching the pull-rod, you will see the rod stop when the lugs on the arm hit the housing. Those are the lugs that need to be shaved. Or some other stop-system engineered.
I'll tell you a secret tho.
I got me a dash mounted adjustable timing control, that made this tuning a ton easier. It has a range of 15degrees. So I set the timing with the device rotated to 50%, that is to say; I can retard or advance the timing up to 7.5 degrees. Then I buzz the car up to cruising speed. I get the throttle up on my home-made stop and let her settle down. When the mph remains the same for a mile or so, then I crank in a quarter turn,or about 3 degrees of advance, and just keep on driving (Manitoba is mostly dead-flat). If the car gains speed, I crank in some more, but if it lost speed then I retard the timing. The goal is to set the timing to an amount that makes the maximum mph, on the throttle stop. Then when you're all done,and if you gained two or three mph, now you reduce your speed back to the starting point, and you are using less throttle to cruise. In this case less is more; less throttle equals more miles per gallon, cuz the engine is making a tiny bit more torque.
Don't drive yourself crazy trying for that last little bit, it's unobtainable using this method. You'll get to a point where 3 more degrees does nothing. Or wait,,,,,,is it picking up speed? aw gee I'm not sure so in goes 3 more and then it slows down. Chit.
So I left that device hooked up cuz my D can only make about 46 degrees at what I have concluded is the optimum idle and power timings, plus the v-can, at my cruising speed of 2150. But now I reset the device so it can retard 3 and add 12; so with the device I can now cruise at up to 46 plus 12 =58* .
The one caveat tho is to always remember to crank it back when coming off the hiway......... cuz 34 plus 12 equals waaay too much power-timing.
To help me remember,I also have an adjustable rev limiter. So when I go on the hiway, I set the limiter to about 2400.This still gets me a top speed of 70 in overdrive. So if I forget to dial the timing back, I can only get that 2400 out of her, and in second or even third that won't hurt the engine, cuz the max power-timing is now just 37 degrees. And when the engine quits revving then the warning light in my little brain comes on.
You can also use this device to help tune the other timing systems.
Then after you think the timing is right on, then you can start playing with the carb.....................And then it's back to timing.......................
The one timing that changes very little seems to be the Power-timing. The iron headed SBMs I have tuned,on road, with adequate compression liked 35 plus/minus 1. And with aluminum heads, mine was happy with 34 to 32