Called up Hayden Automotive. Tech support connected me to the guy in charge of these parts and he looked up the specs for me.
O.D 2 and 3/4 inch
Thickness 1/8th inch
There's a Grainger down the street, and they were awesome. Picking up a 10 pack (lol) of Viton o-rings tomorrow. Will comment on their fitment tomorrow.
GRAINGER APPROVED VENDOR O-Ring, Viton, AS568A-230, Round, PK10 - O-Rings - 1KAG8|1KAG8 - Grainger Industrial Supply