The engine would be an Allis-Chalmers G-153, 4 cylinder, OHV. Can't help w/the spark plug type. Allis Chalmers disappeared from the market place in mid 1980's so parts are a bit hard to find for a 35 year old unit. But if you contact Komatsu Forklift at (708) 385-0330 (Chicago area) and ask for Scott Eller (General Manger with service/parts background) he might be able to help you or email [email address removed]. Scott goes back to the days of Allis-Chalmers and has a bit of gray hair like me. Make certain you have the serial number - should be on the trucks name plate & stamped in the frame - can't recall where to find it. Spent my first 14 years in the lift truck business w/ A-C before having the opportunity in 1981 to seek new horizons. That is when I first met Scott - use my name if you want John Johnson. Hope this helps.
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