John,
The larger wing on the Viper was with the A/B model blocks 5, 10, 15, and 20's. It was 21.5 inches longer than all C/D block 25, 30/32's, CG/DG block 40/42's, CJ/DJ block 50/52's. That wing was 31.0 feet for a wing span.
Do you have a reference for that info? Working at LM Fort Worth with folks that worked early and late model F-16 Flight Test, I asked and cannot find anyone that knows anything about a larger wing (apart from the XL). The big tail & big inlet mods are well known, but nothing on a 'big wing'. The 'beer can' or 'Donkies D*ck' RWR antenna was one visible wing mod, starting at Block 30D
From F-16.net
Externally, the F-16C is almost identical to the F-16A. The only significant external difference is the introduction on the F-16C of an enlarged triangular base or "island" on the rear fuselage leading up to the vertical fin, with a small blade antenna protruding upward from it.
Now, if you were modeling a scale Block 40/42 jet, you could measure the landing gear length
The undercarriage legs were made longer in order to provide more adequate clearance for the two underfuselage LANTIRN pods, and were beefed up to handle the increased weight. The aircraft also has bulged
landing gear doors to accommodate the larger wheels and tires, and the landing lights were moved to the nose gear doors.
Paul