In fact what basic tools do most skoolies use in conversion?
Simple answer - all of them! Over the past week or so more and more of my tools have migrated from the garage to the bus.
The grinder trick worked well. I affixed the grinder disk and then proceeded down the aisle grinding off the front 1/3 of the bolt heads, 2 on the forward leg of each seat and the front bolt on the back. I then turned around and ground off the back 1/3 of the rearmost bolt on each seat. Then I switched to the cut-off disk and cut the the bolt heads. With this method I used 6 or 7 cut-off disks to get all the seats out. The key with the cut-off disk is to take your time and push only directly side-on, any lateral pressure and the disk is in danger of shredding. Oh yeah - wear eye and face protection and ventilate the bus. I wore a respirator and was glad for it.
The outer bolts were clean and accessible so a 1/2" Socket and 1/2" box wrench were all I needed. My bus had seat belts and the seat bottom hinged up for access after turning a latch on the bottom - this made getting to the bolts quite easy.
My angle grinder is a smallish 4 1/2" DeWalt that I bought for about $50 several years ago. A larger grinder would have worked better, you might consider renting a 7" grinder. Be careful with it, use the guard and keep it the hell away from your clothing.
Many years ago I got my shirt caught in a big grinder and it climbed my chest, wrapped itself up in my shirt with my hand still clamped to the switch. It ended up at my throat, jammed and humming evilly, straining as though alive and eager to bite into my flesh - um sorry, I'm little too into the Dean R. Koontz novel I'm reading I think!