Question to the OP:
Are you hoping to preserve the paint on these? If you are, putting them in an ultrasonic cleaner will strip all the paint off, so you can't go that route.
Actually, I've found the paint on most brass locos to be quite robust. I placed two of Chris' three locos in an ultrasonic cleaner with no ill effects whatsoever, not even to the lettering. I think it may depend on what you use for the bath; my choice is heptane (a.k.a. Bestine). It did a really good job of cleaning off most of the dirt, oil and gunk, although it didn't remove all of the rust. I tried a few different solvents on the rust, including acetone, and while acetone put a dent in the rust patina, it didn't clean off all of it. I found that the only way to remove all of the rust is mechanically, i.e. with a soft wire brush--which, of course, must be used with great care.
In the case of these particular locos, the paint was only removed in the ultrasonic cleaner if had been blistered by the fire--and even then, just a little.
