When I ran lines on my '37, I went inside the frame rails where I could, then along the sides when I had to cross over. Nothing under the rails or crossmember, never know when you might stick a jack under there. The length won't matter if you have to go the long way around, once full of fluid, the pressure will be the same. Welding small tabs to mount is OK, better then going through in my opinion, and use lots of clamps to keep it secure.
