Created a simple jig to have the wing fitting hole sit the required 2-1/8" beyond the spar.
Scribed a line 6-1/8" up from the bottom on the main spar and 4-3/4" on the rear spar as being the centre height of the fittings.
Lightly clamped the jig to the spar with a bolt passing through the fitting and then raised or lowered it until the scribed line was sighted right in the middle of the fitting holes before firmly clamping the aluminium and jig.
Drilled 1/4" holes, 1/8" deep into the spar which were used as guides for the next jig...