If he was running LCI engines, then they were not Sirio. LCI works with Rossi engines. If they were Sirio then they have to be LCM.
BTW you can also constantly blow plugs with bad fuel and/or wrong co´mpression ratio,not necesarily conrod or piston failure. At any rate the only one that can answer that question is Josh himself. Lets not jump on to conclusion so easily.
AFM