I've ran crager SS wheels on my 69 swinger for a long time and you need to use the special lug nuts that counter sink into the wheel itself. Don't think over the years I can remember any long studs on a 4" bolt pattern rear end as at that point we would upgrade to a larger bolt pattern as well as other axel's. Maybe something like summer brothers etc. Never had a problem with the correct lug nuts that were supposed/supplied to use with the cragers. Not familiar with the 61C part ?? Probably a manufacturer number ??
Also you say these are the drilled 5x4 bolt circle. Not sure what you mean by that. Did someone drill them or the manufacturer ??
I can post a picture of the specific lug nuts later if needed.

Good luck