I put Disco seats in my 2a. They are bolted straight through so to take them out you have to drop the fuel tank out.
On mine to do this i do the following:
Remove the back of the Disco seat so i can access the filler pipes for the tank and disconnect these
Unbolt the fuel tank and gently lower it - the cables are long enough to lower it onto a box, but probably not onto the ground, but this will give you ample room to replace your sender