To make the Green Mountain Barrel drop into the Investarms stock you might have to take a file and trim the hook or the tang (your choice). You will find that the hooked breech is "just a little thick" to slide in there and lock up. Also you are going to have to take some of the thimble rib off. Other then that the rest is easy. They are a great shooting barrel.

It sounds like you have some excellent rifles there.. You should be all set. Welcome to the forum.