Lee Weldon stretched one and sent it to me for 'tweaking'. I don't know what chassis he started with, but this is how it was put together inside. I don't think there is any chassis that is the exact length.

Link:
http://www.randgust.com/LWmetro1.jpgThe short-wheelbase trucks have inside wheel 'plates' that contact the bushings on the inside of the wheels. Just not as effective as end axles for pickup, but I don't think Tomytec has a short-wheelbase end-axle mechanism any more, hope I'm wrong.
And if you intend to run one hard the stock Tomytec motors are not particularly industrial grade, I've worn the finger brushes out on a couple. I'd refit with Atlas or Kato if the model was intended to be a long-term runner and not a display item.
The driveshafts are custom fitted to length with K&S tubing, telescoping, so when you fit in the motor and get everything set, you ACC the tubing joint and you're set.