Some of us dinosaurs still remember pushrod engines...question; is the pushrod setup, with a gear driven cam, more reliable over the lifespan of a well maintained motor[albeit less efficient], or is the overhead cam more troublefree?
I've recently had my share of woes with a chain-driven overhead cam on a mercedes diesel engine.
I believe many of the large tractors are pushrod...why?
I owned a Volvo B-18,pushrod, gas, years ago...put 500k on the engine, and retired it because the body had metastatic carcinoma[rust].
I kind of miss doing valve adjustments...touching the heart of the iron. Forever listening.