[Andy]

You should not have to remove the tank. The new sender should go thru the hole in the floor. There are baffles in the tank. You need to check for swing clearance with a piece of wire. I would run the float arm to the rear of the tank. The flange holes are drilled so the sender is only clocked one way. I used gaskets to determine the hole pattern.
Edit I put put one in with the tank in the car.