The angle iron is an old bed frame. I just can't pass up a bed frame on the curb, and living in a university neighborhood, I get at least two good crops per year.
The front plate and diagonal plate are 1/8" x 2" steel.
Construction proved a bit tricky, at least for this amateur. I did a piss-poor job of boring the holes for the big bolts in the angles. So I oversized those holes and had a machine shop drill proper holes in some small pieces of 1/8" plate, using the PPF as a template. I felt like a weenie, farming out such a seemingly simple step, but I was getting pretty danged frustrated with the part, and it was $20 well spent to get things back on track.
I then clamped the front plate to the rear bulkhead of the frame, bolted up the angles and the holey plates, and did my best to mark where to cut off the front of the angle irons. I made several iterations of this, trimming them a little long as the fit got closer.
I designed it so the pinion flange would be perfectly vertical, to match the transmission yoke. They don't need to be vertical...they just need to match. But, not having a clearer vision, I figured vertical was as good as anything.
I then tacked the front plate to the angles and the holey plates to the angles. I then removed it all, and fully welded it all.
I added the diagonal last, being a bit unsure if just the angle iron was enough. I thought of doing a full "X", but went with just the diagonal that will be under tension under acceleration. I don't think the torque of downshifting will be as severe.
I then welded a similar piece of 1/8" plate the the chassis to mate with the front plate. (No...I think I put that on the chassis first...yeah, I musta)
I then drilled four holes through both plates to bolt them together. This proved problematic, as it was impossible to drill straight through the plates, with everything else getting in the way of the drill. If I had to do it again, I would have match drilled the two plates first, tacked one to the frame, bolted the other to it, then fabbed up the diff bracket to that.
This approach worked well for me. There are enough odd angles and close clearances, I don't think I could have done it from measurements and sketches, without constantly fitting it on the car.