you can try it, I think that you might find that it takes more heat to un-braze than you would expect. I would cut the down tube/top tube out, leaving enough on the head tube to use that piece complete. Then remove the tubes at the seat tube. You want to check if they used pins, I have no idea if that kind of bike was pinned, but it will make removing the tubes unlikely if not removed. You can just drill them out if they are there.