I received a response from Sonex today. I sent pictures of my work on the horizontal stabilizer and they verified I’m on the right path. As for the pre-drilled holes not lining up, Sonex believed the holes were not off significantly and drilling them out would result in a slightly enlarged hole in the rib flange. I could then make a rivet washer out of .025 or .032 material and put that behind the rib for the rivet head to capture. Then add one more hole between each of the rivets in the rib.
The other option was for Sonex to send out replacement forward spar channels. The forward spar channels are held in place with 27 rivets each. I’m concerned that drilling them out could result in enlarging even more holes.
So today I placed an order for a sheet .025 6061T6 from AircraftSpruce. It was only $10. I figure I can try and make my own ribs that will have the holes exactly where I need them. I’m not happy with the placement of the hing on the rudder anyways, so I’ll order a new hing as well.