Balance is one of the important issues, as would be stability when moving over sills and up or down slopes.
Also, do not use low-rated wheels - probably no less than 500lb or 600lb load-rated wheels (each wheel) should be used?
An SM420 weighs around 150 lbs (without u-joint/housing).
A 216/235/261 stovebolt engine weighs around 600 lbs (no manifolds or peripherals).
