When I wore a younger man's clothes, I used to drill holes in 1/25th distributor caps "by eye". Those eyes are now 65 years old, so with the help of a machinist buddy we came up with this jig to evenly space those darned 8 holes with a coil wire hole in the center.
On the opposite side of the jig is a center through hole to locate the coil wire hole...then flip over the distributor (3/16" dia stock) and put in the "pointer", work your way around with a pin vise and DA DA!
It worked.