Crager S/S on my '66 Dart

I have a '66 with large front drums and I tried to put a set of S/S rims on this afternoon and my studs were too short. Does this mean the wheels have too much back spacing or is is standard to have to extend the studs with these wheels?

Anyway to measure backspacing on these things?

They are good looking wheels and I picked up real cheap, I hope they will work. Thanks.