I prefer to grind the spacer with the pad as well (epoxied together). That way everything lines up perfectly, and it will never shift. It is much more difficult to get everything to line up, and stay lined up, otherwise, and any misalignment will look horrible.
Every professional stock smith that I've come across does the same thing, unless the customer requests otherwise.
I clear epoxy the spacer to the pad. Should I ever take the pad off all I do is get a thin putting knife and tap on the side inside the grove with a hammer and it pops right off.
I epoxy the spacer and use a jig that's available from Brownells. Just follow the directions that comes with the jig. I don't use a belt sand. I use a 12" disk sander with 400 grit paper. You are not going to whack the stock because you are grinding the pad on the jig, not on the stock. Grind to and not beyond the scribe mark. Once you are really close with the sander, screw the pad to the stock and finish it off by hand using 400 grit wet paper on a sanding block and use Vaseline (not water) to lubricate it. I use 1" masking tape around the edge of the wood to protect it in case I fail to keep the sanding block square during the finishing process. Clean up afterwards with Hoppes #9 on a rag. This ain't rocket science. There are probably some youtube videos on this as well.