Your gasket failed due to wrong one...keep the block and use a std head gasket...proper sorted Probably blew on that cylinder cause it to run lean as all other pistons look mint (so not mapping)

Greys dont need to be mapped imo...i had a collins chip for greys and a did the AFR and ok had a 7% co at idle but once running was very good imo flat out in 4th holding around 10.9 which to be fair on an off the shelf chip pretty good

If you was running a lo comp chip in a higher comp engine then it would be very safe due to less ignition advance used....infact you could have run it on 80 ron fuel