I would begin by using the Transformers Customs and Kitbashes Forum. http://www.tfw2005.com/boards/transformers-customs-and-kitbashes.html
Have you heard of that stuff you use to seal gaps on tiles? It's like a putty that dries rock hard or something. Its perfect for remoulding and even molding from scratch. Unicron.com have some awsome Beast Wars modifications on their site using this "putty".