I'm with everyone else. Keep your 05 unless you've got the scratch and are gonna get a daily to replace it. The 68, while a nice car if truely mint (IE numbers matching, etc) MIGHT be worth it, but not for me it wouldn't.
Throw $18-20k in cash on the table and see if he takes it. Otherwise I'd walk. Not too sure of the value of 68 Firebird (Pbody probably would though) but $36k for what you're looking at seems awfully high to me.