I'm probably overthinking this, Just checking to see what width you have for your F-705B center section bar. End to end. (for the rear spar fork). Did you trim lots of material off the outside ends of the rear spar fork when you fitted the wings on?
The plans call for 45 3/32" however I'm more closer to 45" just the way that I have done things. (I made sure I had 1/2" edge clearance first on the inside hole of the F-705C doublers, then measured over to the 12 1/2" and cut both the F-705B and 705C together after it was match drilled.).
Really I am only ~1/32" short on each end so I should have lots room to work according to Section H-H on Drawing 38.