For the most part they all bolt right up (door skins, rear grill, etc) because the two are pretty if not entirely interchangeable regarding the body. Every once in awhile on Ebay someone comes along with a 348 converted to 355 style. I would assume cost would be based on the price you could get these parts off a 355 (maybe TRutlands, ferrari parts exchange, dennis mccann, etc could help with that; dealership would be pretty costly).