I would drill the vent out with at least a #50 drill bit for a .070 hole. You could possibly go up to a 5/64 however, I've concluded that a #50 drill, as recommended by the masters I learned from, was good enough for my standards.
If the original touch hole gets worn out (not in your lifetime) someone can then open it up and put in a liner. I don't have any liners on my guns and the whitetails get whacked by them day in and day out. Biggest culprit associated with failure to fire...garbage flints.