[lintmann]

Yes thanks, that helps.

For anyone else that's interested, I found out that the standard size rubber spacer for 67-71 firebirds and 68-74 corvettes(with aux hardtop) is p/n 4871330 and measures 3/8 x 1/2 x 1. I got this info from my old parts catalogs. I don't have one for Lemans/GTO but I would assume it will be the same. If someone has a parts book to verify it would be interesting to know. Regardless, the "magic" number seems to be 3/8" thick based on this finding and what was mentioned in the link.

Thanks again!