Usually a stuck lifter will clatter a bit. Also, you would be able to spin your pushrod when the valve is closed, because the lifter isn't pressing it up like it should be. I have even measured how far the pushrod is sticking out of the head when the lifter is in the base circle (valve closed, lowest spot). You could pull the side cover off, pull the rocker off, remove the pushrod, then the lifter. Might want to measure lift as well, make sure that you didn't round a cam lobe off.
