So here it is: not a bad little engine, really. I did decide to leave the handrails in their raw brass form (and substituted brass wire to get the full effect), thinking that might be a good look for a well-kept turn-of-the-century express engine, but I'm not wholly satisfied by the look: it's a little toylike, I think. But the trailing truck worked out well. It required no modification; in fact, the engine ran much better with it than it did with the original truck, probably because that bar I thought I might have to replicate on the replacement truck shifted too much of the engine's weight onto the lead driver. I have to admit that I never counted on the simple possibility that the design might be bad, but it worked out well, and the engine is no longer slippery.
As initially built, it ran poorly - it shook, and the gears ground, so I disassembled the engine and removed the motor, gearbox and motor mount. Then I slipped a small piece of notebook paper, folded over, between the motor and the mount, and this cut the vibration and noise way down. Now it runs well, and creeps right along; at some point I have to paint and weather the motor mount, but I'll get to it in good time; for now, it's just nice to have it running.
A few other improvements: I'm going to replace the lead wheels with spoked wheels, which always add a certain period flair. The arch-bar trucks on the tender are going to go, too - I'm waiting on some PSC 4 wheel NYC-style fabricated Commonwealth trucks that look appropriate for passenger service, and I'm considering taking a mulligan on the tender paint job: I'm not totally happy with the decaled lining-out, although I do like the look. I have a spare MDC tender shell, and I periodically consider redoing it - although that might put me on the wrong side of the borderline between nitpicky and neurotic.
I also made some fairly small modifications to the boiler that greatly improve the look of the engine. First and foremost was the bell; Roundhouse engines generally come with an integrally-cast bell that has neither bracket nor hanger, and looks like a small pen cap sitting on the boiler. A good bolt-cutter will take it right off, and you can file the sprue flush. Once that was done, I bored out a hole where the sprue had been, and a very simple Cal-Scale bell and hanger assembly made a big difference. I also bored an .020" hole in the right side of the cast whistle, and fabricated an actuating arm out of a small piece of brass wire. Before I installed the cab, I bored .010" holes on either side of the backhead space, and ran two pieces of .010" brass wireout of them. Then I installed the cab, clipped the wire to length, and glued it to the bell assembly and the whistle actuating arm, taking care to put a very slight curve in both (a very tiny touch of ACC secures it nicely to the dome, retaining the curve). Then I used an 000 brush to paint the wire a slightly different shade of black, so that it stood out just a bit against the boiler. This was not hard to do, but it added some nice visual interest to the model. I bored a pair of holes in the smokebox ( the rivet pattern and the handrail lines allow you to space them correctly), installed some black-painted classification lights, and replaced the stock pilot truck wheels with some PSC 33" spoked wheels - which give a much more elegant front end, reminiscent of the early Western Pacific ten-wheelers.