Fuel tank question

[Matrix37495]

My front and only tank is leaking. I wanted to replace it with a larger tank, but after lots of looking and thinking i can't justify spending the extra money when i don't need it. Here are my 2 questions:

1-2" sending unit or the 3 5/8" one?
2-Plastic or steel (assuming it's not galvanized)

 

[Matrix37495]

Scratch that.... got off my lazy butt and measured. 3 5/8" and i'm ordering a plastic tank.