The truck is a 1965 C-30 Panel Truck. I believe the wet-up would be "stud piloted" as the wheel does not rest on the hub, the lug nuts have the bevel to seat the wheels. Based on that it seems the answer is to replace the studs with 9/16" studs. What happens if you just bolt them up on the old studs, something bad?

My old truck's still running good, my ticker's ticking like they say it should, I got supper in the oven, a good woman's loving, and even my bad days aint that bad...Yeah, I'm a lucky man!
1953 Chevy 3100 Shortbed

1965 C-30 Panel Truck
1963 C-20 Long/Fleet Pick-up California Black Plate