Paul I'm sure you seen the pics of the ones I did ? However I'll freely admit that was very time consuming and there was a lot of work involved.
Don't try chrome plating, it will rust in the valleys as they can't get in there.
Painting probably won't work either as the extreme heat cycle these are subjected to will defeat most paint, plus the surface is so rough it's hard to get a smooth finish and a rough finish will just let water penetrate the paint surface and end up blowing it off.
You could try ceramic coating, a firm in Warrington is who I use called Camcoat, very close to where you live actually. They do a finish called Cermakrome which is like a chrome finish. I reckon £5 a clamp would be the rough cost. Try and smooth them down a little first if you can, they really are very badly cast.
