building a 7mmstw mag box

Ok as many of you may know you can no longer order the ultra mag length magazine box so what I am wanting to do is come up with a way to build my own the same way savage built theirs. Basically I would get 2 LA mag boxes and cut them and extend them by welding 2 long ends together. What I do not have is the specks to do this with. Any one have the ultra mag length box they can take some measurements for me. I was also thinking about a way that I could screw or attach them together in a way that would make it easier to remove from the action
Matt

is there some other posts for this same topic i am missing