What Andre says is right. If you're careful, and if you can still find any, you might even try a can of starter fluid (either). That stuff, however, generally only is sold in northern states where it gets cold in the winter. If you use it, be careful not to squirt too much into the carb. It will undoubtedly backfire through the carburetor, and the fireball produced can catch gasoline on fire. Make sure you have someone standing by with a blanket to snuff any fire out quickly with.
Another thing you might check is the fuel filter. It might be crapped up with varnish after sitting that long. Also, if the car still has the original mechanical fuel pump on it, that might need replacing. Personally, I'd go with an electronic fuel pump (although you always have to remember NOT to ever leave the ignition switch on for more than a few seconds without starting it. The electric fuel pumps I've seen for that era start pumping as soon as you hit ignition).
Good luck with your Challenger. Post some pictures of it if you can!
