These are a great place to go for ideas as well as parts. Need inspiration? Pick up a copy of "Hot Rod" magazine, and get your drool bucket ready. Like forums, swap meets, specialty shops and, well, any place you might find classic auto parts, the more specific the magazine is to your make/model/year, the better.
The mags are also a great place to go for how-to advice straight from experts. Most have online searchable databases, but if you're a classic car enthusiast, you probably know that there's nothing like holding the real thing in your hands.
The Yahoo! directory is a good place to start in your search for classic car magazines.