Cletrac model K

[mishy1973]

Can a regular gas engine i.e. truck engine be used in place of the cletrac engine on these tractors???

[clueless]

If you've got the time and money to make the necessary new connections, almost certainly; you just need an engine that fits, and fabricate...
But whether it's a good idea depends on what you're trying to accomplish: just get it mobile?? run it occasionally in demos or parades?? actually work it, a little or a lot??
Truck engines can be as different from tractor engines as truck engines are from car engines:
Car: deliver smooth power over wide range of engine speeds thru 3 gears (not counting more recent 4-6 speeds for smaller engines).
Truck: develop smooth power thru narrower rpm range, using more gears as much as rpms to vary speeds.
Tractor, esp crawler: develop smooth power thru generally narrowest rpm range, often designed to develop max power/torque at lower engine rpms than car or truck.
Putting a modern higher rpm engine in might overstrain components built for lower rpms and/or overstrain the engine running it slower to match the tractor gearing ;what was it's original engines rpm designation in the 20's?
Hope I didn't cloud up your day!!