OK, so attempting to cut a square end on the rail with my vintage Makita cut-off saw was a FAIL. I gave up when the breaker started popping and the motor started smoking. I've been using this saw for over 25 years and would like to get another few out of it.
I'll take it to the local machine shop where they have the right tools and can turn this into a $100 project.
I decided not to give up entirely and started conditioning the surfaces I want to use. I began with another Makita, my 4 1/2" corded angle grinder and the 36 grit Cubitron II fiber disks I've been wanting to try out on steel.
That's just getting started, but the Cubi disk is getting big points already. I'm trying to keep the disk as flat as possible without touching the opposite side.
After an hour of occasional grinding (my bench is too high for this and my arms wear out pretty quickly) and having moved on to a 120 grit flap disk:
Yeah, I know the skip from a 36 grit fiber disk to a 120 grit flap disk is pretty big, but that's what I have on hand in the shop on a Sunday afternoon.
I'll take it down to 220 grit flapwheel, then hit it with a conditioning disk. For what I'll use it for, I'll be pretty well set. I'm just flattening and bending metal--usually pretty small or soft--so nothing artistic needed.
If I feel the need for a horn on it, I know where some old spud wrenches are--cut the spud off and weld it to the end of the rail.