Probably meehanite cast iron rather than steel. Yep - looks like a long-radius grinder for CX surfaces. Did you put a spherometer on it yet?

If you don't have a spherometer, an old trick Joe Appels showed me was to clean off your grinder, then spray WD-40 on it and get the sun's image in focus and measure the distance to focus. Not as accurate as a well-made and calibrated spherometer but better than trying to stack up valve shims under a straightedge.

Mike