Wow, how lucky that is to re-unite a pair of guns. I agree with most of these guys.
I would concentrate on cosmetically making them match. As far as the stocks, send them to "The Stock Doctor" to have extensions made for both guns.
I would see if the #1 gun could be engraved to signify the "1".
Other than that I would just enjoy the pleasure of having a fine matched pair of English guns.
Oh and yeah there are several sources of 2 1/2" shells available here so that is a non issue.

Mike Proctor