Ridgefield Highway

Cool site The town that I work for has an ex fire tanker converted to a tri axle. It's a 1970 r685st with a 237. The truck only has roughly 40000 miles on it. But for the first thirty years of the trucks life it has routeenly been run at high rpm's to pump. I would like to adjust the valves but we do not have the engine service manual for the procedure. I found tdc in the flywheel but did not see any other marks unlike newer e7's. Any help would be great.