Wasn't clear to me.
I could scan them, verify critical dimensions (thickness, hole sizes and distances between them) with a dial caliper, draw them up in CAD, and send you a DXF or PDF vector file (either is a format that most fabricators can use). 1/8" plate is easy enough to find, I don't remember if
Henry III was using a particular alloy, but whatever it was might be available from McMaster-Carr. I trawled through both threads linked-to below without ever seeing alloy info, nor thickness. Henry III was working in both aluminum and stainless steel plate. I know the plates I got are aluminum, but I'm not sure of the thickess without getting them out of my stash. If I were to try this out, I'd source some harder aluminum alloy than 6061, but that's just a seat-of-the-pants recommendation.
Here are a couple BF threads on this topic
Rally around folks...a snazzy little project I've started -- the original by
Henry III (who hasn't posted on BF since December 2020), and you might want to look at the post #50 on page 2, concerning possible limitations and #57 (threading of pivot bolt on a NR) & #58 (pulley bolt considerations), #87, #91
Henry III's Custom Campagnolo Nuovo Rally cages -- a follow-up by
mkeller234 about implementation. You might want to look at post #7 and following ones about the quality of shifting of Campy derailleurs with longer cages -- I'm no expert.