Back in that time period the Rossi .15 engine ( with the 10.5 MM crank ) P & L would fit into the Cox Conquest .15 engine. At least I know the Rossi piston would because we used the Rossi steel pistons in the Cox steel cylinders to keep the engines together. The wrist pin bosses would pull out of the Cox pistons trashing the engine; the Rossi pistons would not. The Cox engines ran really good with a few timing changes. We ran the engines in FAI Combat.
Dick Tyndall