No problem with gas residue in the tank, just hook a flex hose up to a tail pipe and let run till tank is warm to the touch. You can then cut/weld/solder with no danger. We usually just cut the pump mount flange out of a donor tank and braze/solder it to the projects tank, this keeps the pump and mount together as a pair. The gauge sender will not be correct so a separate mount for an aftermarket sender is used. Pick a donor that uses the same pressure you need.
