I don't know if you are aware but you can purchase a rivet shave bit for your microstructure countersink. I have used the shaver many times including my fuel tanks. Just let the sealant cure for a few months before shaving. Practice on some scrap first. High rpm works the best. Use an air drill or high rpm corder drill, not a battery powered drill.
Shavers work great, no need to fear them.
Dream it, Build it, Fly it
Paul Merems (EAA Tech Counselor, EAA Sheetmetal Workshop Instructor/Volunteer 12 yrs)
RV-7A (Flying since 2010)/RV-4 (sold 1990)
Tucson, Arizona 85749