Rear brake drum rim interference 77 c10

[jrpontiac]

I got some aftermarket wheel vintiques 62 series 15x8 steel rims from Jegs. 4.25 backspacing. The rear is a 1977 big 10. The rim is hitting the lip of the brake drum. Are the rear brakes on a Big 10 bigger than the normal c10. It is almost 1.5 inches short of going on all the way, basically the length of the lug nut. I took the drum off and it went right on. Anyone dealt with this before and what was the solution. The 15x6 steels I have been running fit right on.