Had the same problem with the touch hole liner when I converted my Frontier 36 from cap to flint. I just ground off the back side of the liner a thread or two, and while I was at it i coned the inside of the liner. The L&R lock is a good sparker. I use French amber flints, and have yet to have failure to fire, as long as the flint is sharp.
I think you will be happy with the conversion, I know I was.