Moving forward in the cabin. Next in line, the seat back rests.

It never occurred to me till now. Actually, Vans moves from the front to the back for the bottom part of the fuselage and then from the back forward for the top and interior parts.
I assembled all parts for the seatbacks and started deburring edges.
You need to cut some various angles to length. It's all pretty clear in the plans on DWG-30.

I decided to start with the F-638 seat back braces. They act like a spacer and support between the seat back and the F-705 bulkhead.

First you need to cut a triangular shape from the side flanges. Its all about weight saving.

Secondly, you cut 4 lightning holes in the web of the brace. Did this on the bench drill with the fly cutter. (God I hate that thing)

All done and ready for next step.

Decided to move on on the top of the seat backs.
Two of the F-736C angles  need to be rounded so that they fit in the top bend of the seat back. See image below.
Moving the angle with it's vertex on the 3M deburr wheel back and forward equally until you get the shape required.

For the side angles to the seat back skin, there are dimensions given on the F-637-L seat back assembly drawing. Clamp the angle to the side and measure.

As this takes a lot of time, and all hole patterns are the same, I decided to copy the holes from one angle to the other.
I drilled everything at #40 to start and will enlarge the holes later once all #40's are drilled and clecoed.

Now clamp the F-637B-L and R angles back in place and use the holes in the angle as pilots to drill the F-637A seatback skin.

For the top one, cleco the angle on the inside when you drill.

Next  is the seat back upper hinge. First you measure the hole pattern on the hinge and drill all the holes except for the two outer holes. Those will be drilled in conjuction with the angle on the side of the seat.

Draw a centerline on the back of the hinge as well. Now clamp the hinge on the seat so that the centerline is visible through the holes you already drilled in the side angles and skin. Measure equal distance left and right.
Vans dimensions don't allow for a lot of edge distance on the hinge for these two holes. I think it would be better to make them just slightly longer so the hinge would almost ready the side of the seat back skin. Now drill those two remaining holes with the side angles as drill guides.

the up-drilled all to #30. These will all be AN470 rivets so no need to dimple anything.

Back to the seat back brace and clamped the hinge parallel and centered to the edge of the seat back.
I agree. you are right, I exagerated a bit on the amount of cleco clamps.