Is there a minimum thickness for a stock sbc flywheel? The fly wheel is marked GM1 L207 8978456. It has some hot spots and needs facing.

gm,
I dont have the thickness specs here at home, but if it has never been done, they are usually good for several regrinds, as long as its not worn real badly. You can tell if it has been ground by the finish on it. A stock flywheel is turned on a latch, and the finish will look like a record, but very fine. A flywheel grinder will leave a very distinctive "swirl" finish that you should be able to see along the edge where the clutch mounts.

Your machine shop should be able to tell you for sure.