Grant,
There are commercially available adapter plates. I got one of these from Altair Astro when we mounted an EQ8 on a steel pier:
https://www.altairastro.com/skywatcher-eq8-r-and-cq350-pro-pier-adapter-plate-443-p.asp
Out of interest, why put the C14 in rings and not just use a dovetail?
James