My good friend Tim Shufflin owner and operator of
www.shuffsparkerizing.com feels the best way to remove parkerizing is by blasting with a media such as plastic or glass beeds. Tim has parked many of my M1 Garand projects. Some of my projects started life as unsightly rusty receivers here is a picture of one which was just short of junk.
Don't hesitate to email or call Tim if you have questions he's a real nice guy.
Bill