Uh-oh, might have problems

[alabama mike]

Drove my old 65 c60 yesterday, had just finished rebuilding the brake system and wanted to do a road test, so I guess I put about 25 miles on the old truck, ran great quiet as a mouse, we'll I went to move it this morning and I've developed an engine noise, I'm defiantly sure its not a bearing, I've had rod and mains turn in engines before and know the noise well, I'm leaning toward a lifter or rocker, I've had rocker studs pull out of heads before, but is it possible to lose a lifter from one day to another? gonna head out and pull the valve cover and check rockers for tightness, anybody have any thoughts? I never seem one develop a noise like this one day to another.