I riveted these rib attachment plates and brackets together and also to the firewall.

Pressed in the little Delrin glide buttons on the sides of the popup tipup cam plates.

I still need wrench and socket access for the rod end bearing and jam nut at the forward end of the popup tipup arms. Made a little sketch of a wrench reaching through one of the ribs to determine what sized hole would be needed to have sufficient clearance through the rib to tighten the jam nut. Min clearance appears to be around 1".

I decided to make it a bit wider. With the need for socket access at the top, where the rod end bearing is bolted between the sides of the arm, I was thinking of cutting an upside-down T shape. However, after starting to lay it out, I decided this was going to look too much like a cock and balls :-o, so decided to go with a triangle shape instead, lol.

First one done...that should be fine.

All four done.

Chris was nice enough to weld up these anti-rotation tabs to the bolts which I will use for the popup tipup pivots. I now need to match drill the anti-rotation bolt hole through the rib.

after doing that, I rounded the ends of the plate some. Here's how it will look when installed.