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A good rule of thumb on torqueing head bolts is to start with a bolt closest to the center of the head and torque them in a circular/spiral pattern, ending with one of the outermost head bolts. Another rule of thumb is to torque the bolts in three steps...in other words, if the specified torque is 75 foot-pounds, torque ALL the bolts to 25, then torque all the bolts to 50, then torque all the bolts to 75. And after running the engine a few hours, and getting the engine well warmed up, it's a good idea to re-torque the bolts...again, in sequence. BTW...most Farmall M's I ever saw used studs and nus, rather than head bolts. Coolant won't turn your oil black...but dirt will. Coolant in the oil will make it look milky. Since you already removed the head, it won't help now...but a cylinder leakdown test would've told you whether the rings or the valves were at fault for low compression. With compressed air applied to a cylinder at TDC on the compression stroke--which would mean that the valves are also closed--hearing air leaking out the intake would indicate a bad intake valve; hearing air leaking out the exhaust would indicate a bad exhaust valve; and hearing air leaking into the crankcase would have indicated bad compression rings. A lack of compression could be the result of an intake valve not opening...perhaps from a bent or broken pushrod, or a bad rocker arm, as well as a leaking valve or ring problem. If your lack of compression coincided "suddenly" and directly with a valve adjustment, I'd suspect valves that weren't closing as a result of improper adjustment [too tight], rather than a "sudden" burned valve or a "sudden" failed compression ring. But then, long-distance diagnosis IS a very INexact science.
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