Even though original 1/2-tons seem to me to be getting rare, I doubt there's any value benefit, Market-wise, to keeping the 216 in the truck. But, there's tremendous value to people like ME, who put a premium on originality.
I figure heck, it worked fine when it was born with the 216, it can work fine NOW.
Lots of those 216s went out the door, there's a reason there's still so many around. Good engine, long-lasting when taken care of, and even when not! And, easy to care for.
Why not stick with it until you have a legitimate reason to dump it?
My thoughts, anyway . . .
-Michael