I like to have between 14 up to 18 degrees advance before top dead center at idle below 1200 RPM and 34 to 36 degrees BTDC max at or above 2000 RPM
If you take the advance plate out of that distributor and flip it over it may have the among of built in mechanical advance stamp on the plate, if it says 14 that means it has 28 crankshaft degrees due to the distributor spinning at half the speed the crankshaft does, if it is stamp 12 then it has 24 degrees. I measure the diameter of the advance studs on the advance weights and then measure the length of the slots on the advance plates and subtract the diameter of the studs and then due the math for how many thousands of an inch it takes for each degree of mechanical advance and then weld the slots up and then make them the length I want for the total amount of mechanical advance I want.
Its been a long time since I did the last one I did so I can't remember now the exact amount of length and how much it takes for each degree of mechanical advance, SORRY