First thing I would do is make a drawing of your box .
Then print out multiple images of it on a single sheet of paper . If you can only get 2 drawings on one sheet , then do 2 or 3 sheets .
Then on the first image , do as old ford suggested and layout a boarder.
American rifles for the most part had modest engraving so look at examples . Take note of they types of leaves and scrolls that were used as well as the transitions from one scroll to another . incorporate
Those designs in your drawings .
Take your time . When you get the first drawing done , don’t settle for it , step down to your next patch box drawing and start another layout. Normally myself I do 2 or 3 with the last one being the one that I incorporate what I like best from the prior drawings ..
Once you settle on one of the layouts , take the time to go back and clean it up . IE work over the transitions , smooth out the curves and work over the modest shading .
Give yourself some time to look over the drawing . Set back and study it .
If after a day or so your still happy with it . Then its time to mirror the image and transfer it to the PB for cutting .
Remember , engraving isn’t just about the cutting . Learning to draw good layouts is the biggest and IMO most difficult aspect .