The painting process for the 253's shell is complete (four coats and some time baking in the sun). It's not perfect having a bit of crazing in the paint, but it's adequate. The color is very close to the original, but has a slight blue caste to the green (apparently this is the color of C&NW green). Being more of a preservation project than an accurate restoration, it's close enough for my tastes.
I re-inventoried the parts and confirmed I have everything:

The lamps and the pantograph are reproductions from JLM, the whistle and the plates are original. I have the original pantograph, but it is so bent up I decided to replace it. I don't think I could get it bent back into shape straight enough to look decent, plus the originals don't have the bar running across the top, which looks better to me. I can always swap it out if I rework it later.
I was wondering about giving the plates a bit of a polish, but I'm concerned about the possibility of removing the black paint. I'll likely just wash them off, maybe lightly buff them, but otherwise leave them as is. Hopefully I can get them back in without breaking any tabs.
The real challenge, as I see it, will be fitting the new headlamps. These have tabs that go down through a pair of slots, which will then need to be bent over to hold them in place. The headlamp needs to fit over the handrail that should go down into a recess in the roof under the headlamp...if you don't get them down into the recess properly, they will cause the headlamp to pitch forward slightly when you mount them. Not a good look, so a bit of fiddling required. Then, of course, you need to do all of this without scratching the new paint. I figure if I'm going to break the solder joints, this is when I'll do it.
Headlamps first, then the plates, then the pantograph and whistle.