I just did one of these on an old Dixie York kit that I fell into. The geometry was so bad on this flintlock that it would have required a complete lock replacement, and the gun just wasn't worth it. I plugged the extra holes with copper wire peened tight on both sides, and brazed a pinch of iron into the jaws of the flint cock, and bored a recess for the nipple. It turned out great, and is a lot of fun when I take it to youth demonstrations, because they can't figure out what it is.
Hungry Horse