That vac advance looks very much like the fargo one.
Hex fitting was loose, i looke inside, i guess thats how its calibrated, adding or removing shims.
If i leave mine connected, it hunts. I checked timing and set it around 8 degrees, connected advance and a minute later it started surging. Pull vacuum hose and it straightens out. Guess i need to vacuum test it.
The older autolite ones are the same style, different arms. Do not loose the spring and shims you need them for the right vac advance curve. I might have one if needed, sounds like it blew out.