The clamps that hold the exhaust to the heater box are at the back of the engine. For stock it consists of a washer and round gasket that slides over the pipe where it comes out of the heater box. The exhaust pipe will be flared and the washer will be beveled. A two piece clamp will go over both the washer and the flared exhaust and two bolts will tighten down to hold things together and seal things. As for your rattle, not having the tin work in place allows the tin covering around the heat exchanger to break loose from the pipe and start to rattle. As time goes by they shake more and get looser thus the noise. As far as your questions on #1 that will be the only way to remedy the problem. As far as the missing tin, try someone that sells used VW parts or look in a few catalogs (Mid America,etc) as some list chromed replacements. On question #2 J B weld and stuff of this sort will not work and will vibrate off just as soon as you start the car. I have patched old heater boxes by tapping the metal back in around the exhaust tube and welding it back to the exhaust tube with low heat on a MIG welder, as you don't want to burn through. If you know how to braise that will work also but will take longer(but slim chance of burn through)
66 Ghia, "Dexter" 76 flat window Beetle
It's not a Car it's a VolksWagon!