I just converted a percussion rifle to flint this week. It had a Siler percussion lock with the same plate as the flintlock and I had always been told that you could swap them out after removing the drum and screwing in a liner. NOT! So I made a new lock from a batch of lock parts (L&R Classic plate, frizzen and feather spring, Siler tumbler, sear and bridle and a homemade mainspring). The L&R plate with just a little trimming fit better than a Siler. Anyhoo, the touchhole was way too high like yours, maybe a bit higher. So I made a temporary liner from brass. After threading, I cut it extra long and slotted it. Screwed it in, filed it flush and drilled the hole as low as I could get by with which put it pretty close to where it needs to be. In my hurry I did forget to cone it, which I wanted to do, but like I said, I was in a big hurry cause I was tired of fooling with it. Might try it out after I mow the yard in a little bit. Might make another one out of stainless later (and cone it).