I finally got the old seat out. This is what is supposed to be left once you remove the seat, right?
I couldn't believe when I looked under the seat and saw that it was welded down. They welded it with the tank in place as well. Goot jorb Bubba.
Now comes the tedious cleanup. The positive side is that they were terrible at welding, so half the welds have no penetration. The negative side is that they were terrible at welding so the other half just blew straight through the floor.
Remember: Wise old Owl says "Don't hug the angle grinder!"