I'm not an expert on value but I do watch the market fairly closely and $39K for that car is too much, in my opinion. The fact it's a 326 and automatic make it closer to $20K. If it fits what you're looking for, and resale isn't a concern than $25K. This assumes engine, bottom, trunk etc. all are clean. This price without those pictures is purely guesswork. The devil on this one may be in the details under the skin.
1968 Pontiac Firebird 400 Convertible - April Gold/Deluxe Black Automatic 1968 Pontiac Firebird 400 Coupe - Aegena Blue/Standard Teal 4 speed 1968 Pontiac Firebird 400 H.O. Convertible - Alpine Blue/Deluxe Teal Automatic 1968 Pontiac Firebird 400 Coupe - Autumn Bronze/Deluxe White 4 speed