Thanks, Lynn. I have seen that the 540/550 type is the main choice for this application, but I seem to remember someone adapting a speed 400, and was just curious whether the concept could be shrunken down one more step. FWIW, the 400s are probably quite a bit closer to the 550 end of the spectrum than the 280 end. Ah, well--I've got a few cars on the shelf I haven't run in years, waiting to sacrifice their good parts. There should be a 540 in one of 'em. I'll have to experiment with this a bit.