This is one of those things that can be seem worse in your mind than it is in actuality. Sometimes we have a plan and when things don't work out the way we planned it is difficult to get past it.
I recently had a problem with my GAD 27 mounting too. I'm mounting mine on the forward ribs. I thought I had it all worked out. I drilled the mounting holes for the GAD 27, GAD 29 and GEA 24 and had the units attached temporarily before I installed the plate nuts. Another VAFer came over (DRAKER) and the first thing he says is that GAD 27 mounting isn't going to work. I had taped over the connectors to prevent them from getting metal shavings in them, but in the process had loss track of one of them. The modules were too close together to plug the connector in. I like you was upset since I had a plan for how all of this was going together in my mind. I walked away from it and when I came back I figured out an easy way to fix it, and yes I have a few "lightening" holes.
So my point is don't make the repair overly complicated. It is a bigger deal in your head than in reality. If you don't want to have to look at your mistake make a doubler, rivet it on and then drill some new holes. Otherwise drill two new holes and install the plate nuts going a different direction.
2020 Donation Paid
Titan IOX-370, Dual PMAGs, 9.6:1 Pistons, FM-150
RV-7 Fuselage in progress
* Cabin Interior - In progress
RV-7 SB Wings
* Both Wings fully skinned
* Fuel Tanks Complete - No leaks finally
* Ailerons Complete
* Flaps Complete
RV-7 Empennage - Complete (a little fiberglass work left)
Vans Training Kit # 2 - Complete
RV-7 Preview Plans
Vans Training Kit #1 - Complete
EAA Sheet Metal Class - Complete