This a very satisfactory bashed Superstreets vehicle, completed except for paint. It is deliberately overpowered and also has reduction gears, making it by far the best SS runner I have ever seen.
The length, a scale 26 feet, was necessary so as to not bump parked cars and scenery as it passes around crowded corners on 16" diameter SS curves. And I wanted it to run very slow: normal SS vehicles run smoothly only at about 20-25 scale mph and up: I wanted less than half that.
Photo 1 shows the completed model before repainting - it is a Corgi bus shortened 2" with a band-saw. The ends were reattached using repair putty - easy to see the splice before I repaint. The chassis is from a Superstreets step van unmodified. The shortened Corgi bus body fits with nothing more than a tiny bit of trimming to two tabs on the front of the chassis. Even with the monster motor, I was able to keep the front 1" of the interior, too, with the driver and steering wheel, etc.
Although the chassis is unmodified, the drive is nearly all new (photo 2) although I did use the original axle and its gear. I've found that generally, the larger the motor, the lower the RPM. So, to contribute to lower speed, I fitted the largest I could cram in the bus. It is from an early MTH Veranda Turbine that had seen better days. It has much more power than the original motor even though it turns less than half the RPM of the stock motor at any voltage. And I built a 3.5:1 reduction gear. The result is that this bus will creep smoothly and steadily at 1/4 inch per second - 15 inches per minute - equivalent to .7 mph. It has a top speed of right at 20 mph, at which speed if the power is suddenly cut it will continue on by flywheel for three feet. I plan to cruise it through my downtown at about 8 mph, a speed that looks really good, and at which it is just phenomenally steady. And added bonus, the gears make a bit of a whir that sounds vaguely motor-like at that speed.
I'm making another identical bus and will paint them as city buses, not cross country as the original Corgis were, and have both cruising most of the time when I run my layout.
You aren't kidding about the overpowered part! 
