The English were 1/2 stocking regularly by 1760's. Of course the early guns don't look like the ones you linked to. There are several books out there that would be helpful but they have been out of print for years and are expensive, generally around $400. search some of the auction house sites for pictures, these guns are for sale all the time there. I find these for sale at gunshows all the time as well, many have been converted to percussion.
I used that John Twigg lock one time and found it incredibly lacking. I could get 10-12 shots before it was time to put in a new flint. I'll never use another one.