tuner hole location

Absolute newbie here! I have done very basic mods (pickups, tuners, bridges, etc), but this will be my first time doing actual guitar woodwork and I need some guidance. Given the extremely low price of some eBay basses, I've been tempted to get one to convert to 8-string, for significantly less...

Hi, does anyone know the following measurements: 1) distance between tuner posts, center to center 2) distance from edge of the tuner post holes to top edge of headstock. I bought hipshot ultralite US tuners with 3/8 posts for my current build. The nut is 4 string with a 1-5/8 " nut width. I...