Don, I've tried to circumvent the problem of drilling the spars with a sort of bracket attachment, this was (as usual) inspired by the method Donny uses except it doesn't need soldering.
As always I can only include a pic of my EIII's installation (it's getting a bit old, I know..) but you might be able to adapt a similar setup for your top wing.

The spars are left intact/ instead the webbing (ply, reinforced with hardwood on inside) is drilled to hold both brackets (top, bottom wires) with a single bolt. Make any sense?

You might not even need any drilling or bolting if you 'wrap' the attachment around the spar entirely. Not sure if sheet aluminium would do the job, the stuff oughta be strong to prevent deformation or 'tearing' at the bend..probably brass or better yet steel/

Fraid I share your 'related area of personal ignorance' with respect to lower wing attachment...