Lug nuts/wheel studs for old slotted mags

I've now collected a full set of four 15x7" Ansen-style slotted mags (two are U.S. Indy, two are no-name from Japan...?) with 5 on 4.5" bolt pattern. Trouble is when mocking up on my '73-up front disc brake hubs the wheel studs are too short. How difficult is it to replace front wheels studs on the later disc brakes?

Also I'm totally lost on what type of lug nuts to use, the bolt holes on the wheels are straight and at least a half-inch deep opposed to my old steel wheels with the shallow concave lug-mating surfaces on each hole.