When I rebuilt my 216, I was unable to turn the engine by hand with all pistons installed and new rope seal. I too was worried, but all seems fine. The starter has no trouble, engine runs great.
I used plasti-gauge and ensure all bearing clearances were right on .002" That rope seal is the likely culprit. In order to turn the crank, I temporarily installed the vibration dampener and used a pry bar in the "ears" to turn the engine.
