It's the replacement boot for 65-66 GS for cars with consolette.
Original part number was 388494. By the time the 1973 parts book came out, it was superseded by 3842926, like the one on eBay.
It's the same boot used in 64-67 Chevelles. The boot and retainer ring are each about $20 from the repo suppliers.
www.gmpartsdirect.com has the boot for under $15.
For cars without console, a repo boot is currently in the works.
