[87 Saleen]

Can it be done? does anyone have any pictures of one?

 

[73XR7]

Biggest i have seen is 17"s. If you go 18's you will run into rubbing issues in the front no doubt, also there is the tire issue where the tire will be so low profile you will lose ride quality.
I own a 73 right now and i have a 67 on the way, the 73 can handle 16's ...so just keep in mind how small our stock wheels are
Good luck!

 

[72cat]

Go this thread, may help some.
http://www.mercurycougar.net/forums/showthread.php?s=&threadid=3764&highlight=*18s*

 

[RickDJones]

Check this site out. It has a limited number of wheels but it will give a good idea of what 18"s would look like on the 68 Cat.

http://www.autowaretech.net/swonline/are.htm

Regards
RickJ