First day of daylight savings time and yet by the time I get home and settled down, it is starting to get dark. Anyway, Took flashlight and tape measure out and it appears that the 4 holer is in the neighborhood of 3 1/4 to 3 1/2" mount hole to mount hole. The 3 holer is closer to 2 1/2" as you mentioned.
All that being said, one of the parts that I would like to see reproduced, is the clips that go onto the ends of the terminal blocks and make them "snap in" for the inner fender.
