The McCoy underfloor powertruck was available with both axles powered. They used two pulleys and a 'spring-belt' to power the second axle. The wheel-base was variable based on the truck sideframes. Al Merris marketed a steeple-cab with two McCoy power trucks. All four axles were powered (sucker weighed 8 pounds!). I have the illustrated parts lists (.jpg scans or .doc) for both. I can e-mail them if someone wants to post them.
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