Started out by trial fitting fuel tank again, since I had read the Sonex tank install instructions since last working on the plane. The instruction say that the tank should fit against the upper side of the glareshield, yet mine has a gap of about 3/16". Called Sonex and Jeremy said that if you install the tank with the glareshield and firewall not completely in place you'll get weird fittings.
Feeling better, I removed the motor mount from the fuselage in order to cleco into place the upper firewall (won't fit with motormount).
Drilled pilot holes in the 3 firewall-to-glareshield attach angles. Located the center angle and pilot drilled to the glareshield and firewall.
Once this was done, I again inserted the fuel tank. Much better fit - appears to be tight up against the glareshield, and it protrudes into the fuel filler box on the upper firewall just like the picture on the Sonex instructions.
At this point, I measured the fuel cap height - the instructions say that most builders have to trim the height of the fuel filler neck to get the cap to fit low enough under the cowl. I'll have to go at least 1/4" trim on the next - no biggie.
Located and pilot drilled the left and right firewall angles.
Up-drilled the longeron glareshield holes to 1/8. Also up-drilled the fuel tank strap bolt holes and the forward upper motor mount holes to 3/16" to support AN3 hardware.
Up-drilled the panel to glareshield mounts to 1/8".
Measured and located the spots for the two aft fuel tank stops that are riveted to the underside of the glareshield.