It could be many things. To answer your question though, yes it won't hurt it to run at 210 - as long as it doesn't get much hotter than that. You may also want to consider that your temp gauge might not be accurate. Try measuring the temp with some other device like an infrared gun.
I had a similar problem with the 235 in my '50, however it was due mostly to a dirty radiator. Had lots of blocked tubes in it. I ended up putting an aftermarket aluminum radiator in it which solved the problem immediately, however my head gasket started to leak not long after that - I attribute that to the fact that it's 66 years old and spent 40 years sitting without any water in the block. I'm surprised I was able to drive it as much as I did before it started leaking, really.
