The pics of the 48C deck shown will not fit your 425. And you mentioned needing a gear box.. ?? Seems to me, you are a long ways away from fitting this deck up to your 425, as the deck shown is a belt drive deck indicated by belt-tightening rod shown.
Good job on the pic posting. Narrowed down our thoughts and suggestions, that should keep you from making a buying mistake.
Keep looking for a 48" deck that fits your 425.. it will have a drive shaft to connect to your PTO and the right connection points for the lift arms and the front draft bar. The one you found is not it!