Only problem with the 216 is the rods stretch easier than the 235 due to the poured babbit. The insert style bearings don't stretch as easily because the babbit is thinner and backed by steel.
The 235 head does have larger runners and flows better than the 216 head, which is an advantage if you want an engine to go faster. But if you have a good 216, run it, just don't drive it turning over 2,600 rpm for any length of time. It will last a long time.
