IMO, Leave the patch box on, especially if it is an original Sharps item. Polish out the engraving or just leave it. That makes your carbine unique in my mind. As long as the magazine tube in not affected then there should be no problem.
The front barrel ring can be bought through Dixie Gun Works. Info phone # 731-885-0700. Order phone # 800-238-6785. They show parts for both rifles and carbines in the 2005 catalog page 163. Rings shown. Note: the ring for the carbine is not listed under the Spencer. But look at page 160 and 161, Sharps parts. The rifle rings for both Spencer and Sharps have the same numbers. In the Sharps section they do list a carbine front ring part # VP0335. Call them, it may work on the Spencer. Spencers are know to share Sharps parts.
Hope this helps.