i'm new to the hasselblad V system.. i've borrowing a 503CW and 2-220 and 1-120 backs.. my questions are: can i shoot 120 film in the 220 backs? are the inserts the same for both backs? is it possible to interchange them mixing up serial numbers? if i get a CW winder, can i still use a strap for the camera? is there such thing as a bayonet to screwmount adapter? which is the best metered prism which can be used with a polaroid back?