fuel tank replacement on a 240 is quite simple.
IF the sending unit is good it is best to cut the hoses without trying to remove rusty clamps and possibly breaking the metal pipes out of the sender.
just cut in front of the metal pipes. there is enough slack in the both hoses to pull them back on and reclamp.

remove the rusty clamps with the tank off the car.

try to the this on a near empty tank for weight reasons

place rear end on jack stands

1. unclip the sender connector
2. cut the hoses as described.
3. remove passenger rear wheel.
4. the only hard part of this job is loosening the clamp bolt which holds the filler neck to the tank. this is why it is easier to see this if the wheel is off.
once you get this loosened
5. remove the 5 or 6 bolts holding the tank in
6. place a jack under the tank so it does not fall straight to the ground out of the frame until you have jiggled the filler tube out of the tank

you will find the only hard part is accessing the clamp of filler tube to tank.

to remove the sender with tank off the car is easy
use a large flat blade screw driver or pry bar and bend the locking ring inward until you break the holding integrity of this circular piece. from there just use pliers and pull it off.

I am pretty sure not many of them have been replaced as I have yet to see a reference to replacing the tank on a 240 in more than a decade of watching these forums. I am no help as a result but I am curious why it needs replaced? Was it punctured or did it rust out?

I am pretty sure there have been some posts for 9-series cars becase a popular upgrade is the later model larger tank but I doubt there is too much overlap between the two cars in this area.