To hold the center part of the frame down, I purchased some stubby clecos. As you can see in the image, they are substantially shorter then the traditional clecos. The stubby clecos will be left inside the frame while I match drill the forward covers.
To get achieve the correct spacing between the forward and aft places, I put some temporary spacers inside the frame. I’ll be able to clamp down on the spacers to hold everything at the right thickness.
I wasn’t able to get to drilling the forward frame, but I did get everything fitted properly. I filed down the center faces of the forward frame so the parts would butt up properly. Now this assembly is ready for match drilling.