GGG-P-463c is the Fed Std for Granite Surface Plates only, and does not apply for steel or cast iron surface plates. I can't recall what the Fed Std for metallic plates is off-hand, but I will look when I get home tonight. As I recall, the specification on non-granite plates was much looser.
That said, it is very difficult to find a company that can measure/resurface a metallic surface plate because it is not cost effective. The process of resurfacing them is very time consuming and very close to artistic. In the hundreds of locations that I have been in doing surface plates, all but one had marked their cast surface plates as "Reference Only" and replaced them with granite surface plates, due to the very well characterized elasticity modulus of granite, the availability of service, etc.
If you must keep the steel/cast iron plates, then you should spec them as you need them, and hope that they never require resurfacing. The only company I ran into that could resurface them used the same method that they used for mill surfaces, which was a hand scraping that took a few days labor. If you are looking for a company to do the plates, then a mill resurfacing company will probably be you best bet, although it may be difficult to find any that are accredited to provide that calibration.
Ryan
I think this would simplify most of my problems with this issue.
