Tried the same technique with a 30" Sign that was bent and folded some. Used a Large compact tractor wheel and plywood to flatten the sign. As you can see it worked well. The condition of the sign is -10 as you can see so I wasn't worried about porcelain loss.

Mary June 011.JPG gas2 002.JPG

I'm collecting all types of porcelain signs but prefer Mobil Oil.