I run 1.25" spacers in the rear of my cobra as well. They are hubcentric of course. My spacers started life as bolt on spacers. I knocked the studs out of them. My car OS fitted with 3" ARP studs for weld wheels. I simply slid the spacer over the 3" studs, through the holes that the studs were pressed into. The fitment is tight, so I am not concerned about them ever shifting or coming loose.