[wagonman76]

I like that better still, the long lugnut with blind hole. Drill and tap the end for something simple like 1/4-20. Of course be aware that drilling and tapping grade 8 (typically all automotive fasteners are grade 8) is harder than plain old mild steel. Itll take more time and patience. And you can get 1/4-20 grade 8 bolts at Lowes or Tractor supply or most hardware stores and they dont cost much.

The best thing would be if the ends of the lugnuts were a hair shorter than the inside face of your flat wheel cover when it is in position. You could use a grinder or lathe and cut the nuts down if necessary. Or if the ends of the nuts are too short, what would probably be easiest is to glue washers to the inside face of the wheel cover until you get the right height. Use JB weld or metal epoxy. Either way you need to make sure you bottom out the wheel cover and bolts onto the ends of the lugnuts, or the bolts will just work their way back out.

Edit: If wheel lugs are not grade 8, then are they grade 5? They certainly should not be grade 2.