Dan. My thoughts are that an even 360 degree firing would do away with the Centa while the counter balance shaft would would help with secondary imbalance. Allow me to clarify that when I wrote 'offset crank pin' that I was describing a single crank pin being split (as used by some V6 car engines). I think a 90degree V-twin would be a better option to do away with the Centa, just my opinion though.
Back on topic;
So it was the damaged camshaft keyway key that allowed movement on the cam cog, which changed the timing, causing the pinging/overheating leading to the cylinder head gaskets to go. The question then is what caused the damage to the key. Perhaps extra keys should be carried as spares along with the usual suspects.
