If you are registered, you get access to the members only section, can participate in the buy & sell second hand forum and last but not least you can reserve your preferred username before someone else takes it.
To be able to focus and set shutterspeeds and apertures, there are rings that go over the focussing ring, shutterspeed ring and aperture ring of the lens.
The ones that came with this underwater housing fit the old C lenses only.
But even with C lenses on your 503 CW: the transport thingy couples to the 500 C/M's wind crank plate, which is different on the 503 CW.
If an underwaterhousing is needed, you will have to look for makers that still produce such things for the Hasselblad gear that is available today.