Thanks for the feedback and suggestions, folks. I took a hard look at all of them.
My objective is to have a sidepipe mount providing both horizontal and vertical location for the tailpipe while clearing the long trailing arms. On the approach I was pursuing, a rubber bushing with a 4-hole, diamond patterned design with no slots between the holes was needed. Turns out the Holden part was the only alternative that has this. I was able to get some dimensions and mocked it up, but the result was too big for the space available, even if the part "shrunk" a bit. So off to another approach.
The C2 and C3 Corvettes had a similar sidepipe issue and used a simple mounting technique. With a little adaptation I think I can make the Corvette approach work and it looks like the mount would fit in the tight space available. And the parts are easily available.
If this works out, I’ll post the results in my build log.
ChanoquinII, casting my own biscuits in polyurethane was a great idea. Hadn’t really thought of that. Very do-able and lots of different resins to choose from. 60 durometer poly-pieces would probably work in this application. I’ll file that one for the future if the Corvette approach doesn’t work out.