Made a little progress the past day or two.
After gluing all of the doublers, wing saddle and horizontal stab supports on I removed the fuselage sides from the board clamped them together back to back and sanded till they were identical.
Next I clamped one side to the building board to attach the fuselage formers. Remember the reference line? It will come in handy with the next couple of steps.
I installed the firewall, F2 and F3 using the reference line to make sure they were perfectly square and then made sure they were perfectly square with the building table. When satisfied I glued them in with 30 min epoxy and clamped in position and re-checked for alignment.
After the epoxy cured I trial fitted the other fuselage side. The second fuselage side is identical to the other, so if I install it perfectly on top of the other side I should be able to place my 90 angle against the sides at any point and they should be aligned with each other. I again used 30 min epoxy to glue the other side to the formers, checked alignment with my square and clamped. Then checked alignment one more time.