AC 44 for light duty use probably will be alright. AC 42 or 43 I think is the original specification. AC C42 or C43, if you can find them are commercial plugs, made for heavy duty operation. The only difference between commercial and standard duty plugs of the same heat range (number) is the commercial plugs have larger elecrodes than do standard plugs.
What ever you use for spark plugs, check the color after a few miles- 50-100 or so. Dark means too cold, too rich or burning oil. Bright white porcelain, like new, or shiney elecrodes mean too hot, or maybe too lean with fuel. A good color is light tan or slightly off-white, electrodes not quite shiney. I know that last bit is not very clear; you kind of learn what the electrodes should look like. A little too cold is better than too hot for a larger truck. Spark plug temperature goes up with engine load and throttle opening.
Harvester
