Hi Doug and welcome. It's possible but here's a couple of things to check out and consider. How will you mount the router to it is first and how thick is the hole where the bit will go through. Most cast iron tops are 3/4 to 1" thick. That wouldn't leave you much extension on many small bits. Possibly not even enough to expose the full profile above the table. If you try to thin that part of the table will you compromise table structurally?
Most of us older guys on the forum build our own tables. It's cheaper in the long run and you get what you want that way. Router insert plates are 5/16 to 3/8" thick so you would lose a lot less of the height capacity that way. I've built tables for as cheap as $5-10 by repurposing materials and they aren't that hard to build. There is a very large and long running thread on tables members have built.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.