To Vacuum Advance or Not to Vacuum Advance

You may already know all this but just in case...

Canisters come in varying degrees of advance capabilties and different starting/ending points of vacuum inches.
You can change when the advance starts by adjusting it with an allen wrench. It will not change when full advance is reached or total advance. So if you crank it out counterclockwise it wont start advancing till 15” ( random #) but it will be all in by 18”... so it just shortens the window ...
The arm is usually marked for the total degrees of capabilities ... 8.5 means 17* of advance when reading the dampner.
I have heard of cans that are not adjustable but I think it is due to a smaller allen screw being used in some.

There are also different advance plates and they are marked in 1/2 crank degrees as well... I dont know why some slots are angled though ? It might allow more advance without having a super long slot or it might be a leverage feature ?
Good info
The distributor I currently have was setup By Don at FBO specifically for my engine. I just started playing with it, yes it is adjusted using an allen wrench.
I am going to leave it as is for the summer, will take another stab at it this fall when time allows. The engine is very driveable at the current settings and pulls like a freight train when your on it. Last tank of fuel (91 Octane) averaged 13.8 mpg, mostly highway 3000rpm @ 70 mph
I dont know how much better I can make it without screwing it up LOL