I have had ALOT of my a-bodies with that problem. Ten years ago, I scrapped them. Now I wish I wouldn't have!! Yours doesn't look to bad (to a guy that lives in Ohio lol). My 66' Valiant actually broke one of the mounts loose on the way home from buying it, made the passenger wheel tend to do what it wanted sometimes. I made it home, it wasn't too scary. Anyway, check this out.
http://autorust.com/store/index.php?main_page=product_info&cPath=2&products_id=395 (might have to copy and past it). It is a complete replacement for the upper mount. Or, you could get a good one off of any 67-76 a-body, and 64-66 a-body (thats all I know for sure, may be others that are the same.) I actually have 2 sets of them here, with the framerails still attached.