It just slots straight in. Problem is if it is a later type you will not be able to use the rear-mounted safety-catch. The early ones didn't have a safety catch so there is no loss there.
Weihrauch do offer the HW50 with the Rekord in other countries as the HW50S (nicer stock too) but not here for some completely unfathomable reason known only to Hull Cartridge. The Rekord is one of the main reasons to buy a Weihrauch as far as I know. Hull Cartridge SHOULD import the HW50S AND the HW30S as it would make them money but they DON'T except by special order.
I suppose you could buy a new end plug and safety catch section from the HW50S, if you specially needed a safety catch, but it will cost you alot of money. I don't think they are necessary pieces of equipment on a break-barrel springer and don't actually make them any safer.