Other folks would probably know better, but why not shoot 2 1/2" shells in both. If it were me, and I thought I reunited a true pair, I wouldn't modify either with irreversible changes. I'd figure if I was putting money into new, not restoration, engraving, why not do it to any old two guns and call it a pair. I really don't mind what someone decides, I know for me I tend find true classic guns less interesting if they have been personalized.