Describing a sound is hard to do. You need to experiment. Your 216's and truck 235's had mechanical (solid) lifters. First set them by the book, .006 Int and .013 Ex if I recall right. Listen to this. Now set them on .012 and .026 and listen to them when they're too loose. It won't hurt them, just noisy. If too tight the engine will run rough and shake and eventually cause damage, not good. These old engines have rockers with wear in the bushings, wear on the rocker shaft, and usually "eyebrow" grooves worn in the rocker from the top of the valve stem all of which means a little noise even when the valves are adjusted to specs. No harm and if it runs good just enjoy it. I have a 37 Buick with the same rocker set up and I guess GM didn't want Buick buyers to hear the tapping so they coated the inside of the rocker cover with about a 1/4" of asphalt like stuff and then put a 1/2" thick strip of felt the length of the rocker assembly. Makes it dead silent.
