Bill Tindall, E.Tn.
This comment comes with all the qualifications of my planing needs vs David's. I have used Blanchard ground cast iron plates now for many years. Blanchard grinding leaves large swirl marks on the plate. And I have some plates ground on a surface grinder to a fine finish. I don't experience any difference between using these different surface plates.

The purpose of this comment is to encourage trying what you have and see if it works for your needs. The level of success on a less than perfect piece of cast iron may be good enough.

The first chisel I Unicorned was 5 +/- strokes on 1 micron diamond on Blanchard ground cast iron followed by 5 +/- strokes on leather with green stuff. The chisel finished a set of 5 ash drawers. If you are selling a drawer where this chiseling is hidden from view your satisfaction with results could be different from plane making.