rebuilding vacuum dash pot

I need to replace the rubber diaphragm in a 1967 Pontiac dash pot. It's a one year only for the Quadrajet. I have it apart and starting shopping for rubber but figured out I know nothing about it. I measured what was left of the old piece, best I could measure was .015" , but that's where it was crimped together.
It does look like it has fiber reinforcement in it. 3" diameter, the " piston" doesn't move all that much.
Anyone know what I should be looking for?

Joe

 

Joe, these guys rebuild vacuum advances and may offer some thoughts on what you need FWIW

Distributor Vacuum Advance Rebuilding - My Cl***ic Car Trader

 

I've think I have it figured out, medium density should do it, McMaster Carr has a bunch of different types, all listed for multiple proposes.