I called Vans Technical Support in the morning when I got up. After reviewing the pictures and some discussion, the best scenario for what I had going on was to clamp the weldment a bit. While it is true that edge distances are not as critical for steel as they are for aluminum, we really want to increase the possible edge distance were we can. It was agreed that too much pre-load was not great, but the consensus is to split the difference as best I could. Excellent...I can do that.
So later in the day, I got to work! I did some edge prep on the gussets to get them to fit a little better against the firewall. Using AutoCAD I re-spaced the rivets to give me good edge distances all round, I then transferred those onto the actual gusset using a #40 drill.
I then clamped all the pieces down. Notice that I have a brace against the firewall. That is to help push a little on the firewall to get it perfectly straight. It has a very slight bow so before I drill the gusset to the firewall I want to make sure everything is straight.
Once happy with the fit, I drilled into the longerons with #40. I then used these pilot holes and used by drill guide from ATS to finish the holes.
Using a reamer, I upsized the holes to #30.
Edge distance is much improved on the left side. I confirmed 0.1875" which I am very happy with.
