Both pistons showed catastrophic failure modes ! The top piston ring locating pins on both pistons had become loose and made there escape via the piston crown... and the right hand piston had also broken it's bottom piston ring, although luckily not damaging the bore.
The pistons themselves have been heavily worked, with additional port lowering on the transfer ports (about 1mm lower) and the skirts have been knife edged with all internal surfaces having the casting marks removed and polished.
Fortunately a new set of original 54mm pistons came with the engine ! again originally from Sonny Angel via the friend I bought the engine from.