"Any way I can distinguish the 216 from the 228?"
Yes! If GMC is stamped on the valve cover it is not a 216.
The gmc family of engines, 228, 248, 270, and 302 have 5 freeze plugs on the left side of the engine under the intake and exhaust manifolds.
If it has GMC in the Valve cover, or 5 freeze plugs, check the flat horizontal surface behind the distributor. The first 3 numbers will tell you which GMC engine is in your truck.
It is not unheard of for a GMC to have a Chevy engine swapped into it, but the gmc engines are a better design than the chevy.
