Depends on which link you looked at, the the first one is with a Winchester M94 hammer extension, requires annealing, drilling and tapping the hammer, you can also modifiy the hammer so the H&R extension sits lower on the hammer. Another option which I've been doing lately is to modify the H&R hammer extension itself by changing(grinding) the shoulder height so it sits lower on the hammer, then just grinding the hammer spur so it's not as tall. One thing you have to be aware of, is if you get the hammer extension too low, it will hit the barrel release.
There are a multitude of options, you just have to figure out which way you want to go. Depending on the scope and how much you remove from the hammer spur, you can go as low as extra low rings sometimes, yet other times, you don't need to change the hammer at all. I've mounted a 6.5-20x50MM Simmons WTC18 in medium rings without any changes due to the small power ring and position of the scope.
Tim
