I was having a devil of a time getting the holes in the drums to take the tap for the pant mounting screws. In fact, I couldn't even get one hole to take the tap. So I decided to go with Rivnuts instead.
I installed 3 Rivnuts (photo 1). In previous posts you'll note that the gear leg interferes with the locatino for the 4th fastener, to the point that there would never be any way for me to get the fastener in or out. So I'm leaving it off. I'll just have 3 fasteners per wheel pant.
Photo 2 is the wheel pant test fit onto the drum.
Photo 3 shows how the backing plate is well ouside of the drum when the Sonex-supplied axle spacer and the wheel assembly are installed. I've sent an email to Sonex to ask if this is the way it is supposed to be.
3 Rivnuts installed. Rivnut installer to the right.