I know some of those crazy guys.� Jeff Petrovich (JPet on the forums) has crushed that muffler almost beyond recognition.� He is who I was thinking about after reading your post.
What you're thinking of doing is perfectly reasonable, but I don't think the exhaust in its current position would ever get hot enough to melt your tank.� If you're worried, you could attached some modern style shield plates between the tank and exhaust.� That would probably be cheaper than a new MB style system.�
If you do the modification, let us know how it goes and how it turns out.