I've got my 66 unibody on a dolly which has big rectangle plates that cover up the frame where the round unpainted support marks are. I plan to make some disc to slip over the post so when I paint the undercarriage it will leave the correct size circle unpainted.
If anyone can tell me what the correct diameter is of the factory support pad is, then I'll be able to make the disc up without having to lift the car up off my dolly just to inspect and measure what I can of the original marks.
Metuchen car if it matters.