That one looks home made.

Cosmo had one that best I can tell was profesionally/comercial made, or if it was a one off it was a superb job. Probably aftermarket and not GM, but looked factory made in every detail.
Perhaps he has pictures of it?

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
---All pictures---
"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-