250's have hydraulic lifters, so they're adjusted just like a small block V8. Get each cylinder to top dead center on the compression stroke, gently take the slack out of the valve train by spinning the pushrod as you tighten the adjusting nut, and add an additional 3/4-1 turn of the adjusting nut after the slack is taken up. Adjust both valves, then move on to the next cylinder in the firing order. I use the companion cylinder valve adjustment method, but nobody else seems to be interested in doing it that way.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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