I'm assuming you mean the pushrod was displaced, not the valve, right? Most likely, the valve stuck in its guide momentarily and allowed the cam follower (AKA "lifter" or "tappet") to get disengaged from the rocker arm and pushrod. I'd suggest adding a quart or two of Diesel fuel to the sump, overfilling it enough to make the crankshaft and connecting rods splash down into the diluted oil like a washing machine agitator. Run the engine at fast idle, 1500 RPM or so, for about 15 minutes. The diluted oil will clean out any gum or varnish that has accumulated over a few decades, including any deposits in the valve guides. Drain the oil with the engine hot, replace the filter element if the engine has one, and refill with fresh oil.

DO NOT DRIVE THE VEHICLE, OR PUT THE ENGINE UNDER ANY LOAD WITH THE DILUTED OIL ONBOARD!
Have fun!
Jerry

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