I don't normally comment on others mods for their steel,but having used the Ts-85 for beaver,which is what it was intended for,I don't know why you'd want to 4 coil it.A properly caught beaver is not going to get out with factory springs.Maybe a need for it if you're trying to make a wolf trap out of it.
Not the case. We had them empty at the end of the drowners more than once. There was a video on here once of a beaver getting caught in one high on the back ankle but the trap was empty when they checked it. If you look at the catch pictures of beavers in TS85's you'll often see where they were caught higher but the trap slipped down the foot, sometimes all the way to the toes.
4 coiling IMO is a good idea.