If you're assembling it yourself from parts this is easy, just saw the bridle from the pan and drill and tap the plate for the screw. If you're using one that is put together it becomes a bit more complicated as the frizzen is already hardened and the plate is drilled for the clearance drill and countersunk for the screw head. You would need to anneal the frizzen so that you could drill a larger hole in it and drill and tap the plate for the oversize screw. I think there should be enough thickness in the plate and bolster that the countersink for the old screw head wouldn't make much difference but you could always silver solder a piece of steel in the countersink so that your screw could have threads entirely through the bolster. Because you would need to anneal and reharden the frizzen to enlarge the hole, it would probably be easier to just get a new, unhardened frizzen from Chambers.
Tom
