Help purchasing a new fuel tank/sending unit?

I have a 1973 Duster, and there are a few things I don't get?

First how many vents, second I have "heard" if available to go with a "larger" sending unit, 5/8 instead of 3/8's or whatever it is?

Do you just cut your own hose to fit, or is there exact size?

Does anyone know where to go for this stuff for a good price?

Thanks!