To start off with I went through my Track Of The Wolf catalog until I found a side plate I liked. Handily, their parts have life sized pictures. Then I traced over the side plate and used carbon paper to transfer its outline to a piece of paper.
After I had a good outline that seemed to fit well on the stock I cut it out of a piece of steel then started grinding to a closer fit. In the picture here the plate is still a bit too big. After I drilled the holes in the plate I further trimmed it some to make it fit nicely.
I choose to use steel over the traditional brass for one main reason. I didn’t have any sheets of brass laying around, but I did have steel laying around. Some guns were actually build using steel hardware so its actually not fully incorrect historically. Most importantly, it was good practice for me in building a plate that is the proper size.