I couldn't help myself and changed the shape once more, but its done now.

had made six 38 pin female headers as crossbars for support.

Pull the pins

Chop it

Sand it.

I had 220 sand paper. I would have preferred higher like 300.

I just eyeballed by hand it every few seconds to get it square.

The ends won't be seen anyway. They will be glued inside.

I really wanted to make a thin wooden base for this. Instead I had two thin plastic CD cases that just seemed to fit just right as a temporary base. Three headers on each make two 120 pin sockets (almost) to access the inside.

Update:

Super glue worked well at first. The cheap stuff gives you a little wiggle time to position correctly. The top split apart a few times at weak spots. Most of the glue joints did well but several were stubborn, even after sanding, as if something spilled on those. I got a Loctite's "Plastics Bonding System Fuses hard-to-bond-plastics" super glue with separate primer/activator. It fixed the stubborn ones, but no wiggle time at all.