The key is to have a new sending unit gasket to prevent fumes in the cab.
If you were ever in a wreck so severe as to rupture the tank behind the seat, you would not likely be around long enough to know it.
I prefer the '54 style of sending unit, especially on a used tank due to the potential of 60 years of debris which likes to move to the hole in the bottom of the earlier gravity feed tanks.
The '54 pickup is slightly off the bottom of the tank and comes with a decent sock to keep it from clogging.
Carl
I like the idea of the 54 sending unit also. So I would use hard lines inside cab right? What about capping off the gravity feed? What's the proper way? Should I seal the tank after cleaning? Minor surface rust inside and out, patches really and looks like old deposits in tank.