Do you have all the SE specific parts (backglass, backglass plug, vinyl top trim)? If not, I'd seriously consider just building it as a regular challenger. SE stuff isn't terrifically expensive, but some of it is difficult to locate. The nice thing about 318 cars is that you can build them to your specifications without feeling too guilty about it. Rebuilding/restoring a car to ANY degree is preferable to just letting it sit outside rotting away.

Congrats on your purchase!