I broke a couple of very small endmills cutting those ports. I had expected this: I had gotten spares before starting the job.

The ends of the ports are not round and aren't square either. Since they sit under the edges of the valve, it doesn't matter: port widths are critical to timing and steam distribution, but the ends aren't.

The matte gray finish was left by lapping the face on an iron lapping plate. They say that that's a waste of time, because the valve and face will wear in quickly whether or not they've been lapped. It's probably true.

Those grooves out beyond the ports were suggested to me by someone on the Model Engineering mailing list, God bless'm. I was close to putting the casting on the shaper and lowering the entire face except for where the valve actually rides. Lots of extra work, and it would have changed the position of the steam chest, leading to other complications. The grooves were a simple solution.

I don't know which way I'll do it on the next engine. No problem with making a raised valve seat, if one plans for it beforehand, so maybe I'll go that route. Still, it's extra work and probably isn't any more effective than the way I've done it here.