We had to grind on our Minnesota bus. There were 4 Grade 8 bolts per seat on the aisle side and 2 on the rail on the wall. Aside from maybe 3-4 on the side rail, all were removed with wrenches. The bolts on the floor were NOT coming out though.
It takes a while, but with the radio playing and someone to talk to it isn't all that bad. I did manage to kill my old cheap grinder doing the project, but it had served me well so I wasn't disappointed. I purchased a new cheap grinder with a 1 year warranty to finish the job. Because of the shape of the feet on our seats we had to actually grind the whole head off, but it went quick with some think grinding (not cutting) wheels.