how rare is an 1976 duster 360 sunroof car !

Your car being a Duster means that it cannot be a Hang 10... those were all Dart Sports and only in 1974 and 1975 IIRC.

It could be a Spirit of 76 edition though... they had a red, white and blue colour scheme. Regardless, any Duster with a 360 in 1976 would be a rarity and the sunroof makes it all the more so! I'd say keep and restore it! :)