Ordering the stock always determined that indeed the building project was underway, and this was not a matter of simply buying expensive kindling wood! You have made the project a serious commitment, and a flintlock shooter is down the road, and I wish you well with each future, pain-staking step.
I might suggest something for you to consider. I built my .36 cal. squirrel rifle several years ago, and it turned out well with one bothersome short-coming. If I were to do it again, I would change my selected 42 inch barrel choice for a 39 inch one. There is a lot of steel in that 42", .36 cal. barrel, making it uncomfortably front heavy, in my humble opinion.
I use this rifle during the fall turkey season, and readily admit that by day's end I'm glad to slide it back into it's wool case!
As a lefty myself, I can appreciate your desire to work on the lock and side plate inletting yourself. I use the dremel tool with extreme care inletting the lock, and although not historically correct, find it provides a neat and precise job of this all-important task.
Best of luck on your project, and best wishes for many enjoyable years in the squirrel and turkey woods!