I had already built my vertical when I did the showplanes stab mod. I drilled out the existing rivets, reworked the stab skin, machined a little off the nose of the rib and made it fit. Its adequate.
I think the better solution is either make a new rib like Dan H, or obtain a new blank rib from Vans (no pre-punched holes) and 'adjust' it to fit.
Robert Grigson
RV-8 Showplanes Fastback, Currently firewall fwd