Can you weld or are you taking that somewhere to be installed? I know a lot of shops will not weld sumps in used gas tanks anymore..I cringe a little but do them, usually I am using a BBRC tank.
If you going to weld the tank, sit the tank outside with Simple Green or Mr Clean in it, full of water for at least a week to try to kill the gas smell and fumes...
I also weld the tank with water in it..
Now, that sump will work witn no issues. What pump are you looking at running, that will determine mounting. I use Fuelab external pumps on my systems and mount them off a bracket on the bumper, at the same level or slightly lower then the sump feed fitting. Most external pumps are made to be gravity fed.