Larry, I can't speak to the 216 but can a 235 if you want to draw a comparison. The picture that Tim attached is a good reference. The various oil feed connectors before 1959 had a return loop where Tim's picture shows the pinched end. They were designed to allow enough oil to flow to the rocker arms with the excess returning to the oil pan through the pushrod holes.
Many owners/mechanics pinched off the loop on the return side to force more oil to the rocker arms. The oil still ends up returning through the same path, just more goes through the rocker arm shafts to the rocker arms. This was a very common practice.
What I find interesting is that in my experience, more 235's have had the fitting pinched off than have been left original. It is much harder to find an unmolested one than a pinched off one. A couple years ago, I was helping a fellow 'bolter find an unmolested one, so I went looking in my usual spots. I checked about twenty engines at a couple different yards and only found two that were unmolested. Maybe that was a fluke, but I found it to be interesting.
Would you hurt anything by pinching it off? Probably not. You'd force more oil to the rockers. Is that how the GM engineers designed it? Nope. Have thousands of people done it before? Yup. The only risk that I would see is that you might slow down the rate/volume of the return oil by forcing it through the constrictions on the rockers, but if that was a problem, I'm sure the practice of pinching the line would have stopped long, long ago.
Want another worthless bit of trivia? I've seen two different ways to pinch off the line. One way was to cut it off close to the top of the loop then crimp the cut end in a vice. The other way was to leave it intact and use a cold chisel or a crimping tool to notch the line at the top of the loop. Maybe for aesthetic reasons, maybe for performance, maybe didn't think about it too much, dunno. But I've seen both ways, so I decided to test them. The ones that are cut and crimped in a vice aren't completely sealed, but barely allow a drop of oil to exit the crimped end. All the oil has to flow through the rocker arms. The ones left intact that are notched are not sealed as tight and still allow some oil to flow through the return loop as intended, but restrict the flow so that more goes to the rockers.
Leaving the line intact and notching it seems to be the best hybrid approach IMHO. Not sure that it matters. That's what I have on my 235.
Starting in 1959, the return side was pinched off by design because the rocker arms were changed to offset oil grooves and the pinch helped to pressurize the shafts with the new design.
Probably too much info for a simple question,
Matt
