It was common to put plates in the neck section if you were molding a frame for a chopper/custom back in the day. Kept the amount of bondo to a minimum. (Ask me how I know
) I wouldn't grind the plates out. I'd get your torch out and just melt the braze off. You can use a scrap wire brush to remove it. I say scrap because you will ruin the brush, but you can usually get just about all of the braze off. Good luck and let us know what you find.