Many thanks to those who contirbuted and also general info for others
All went well and the inbound flight arr 15 min early into LAX, and the transfer was very well handled, cases went through MEX - LHR, without needing to be collected in LAX and dropped off at check in. Son and girlfiend, by now fiance, met at plane by Mexicana staff and escorted through immigration, who were surprisingly friendly!! and fast tracked to the NZ2 Gate, via fast track security in T2 with ample time to spare, NZ2 left 30 min late and arr LHR 45 Min early.
Well done Mexicana and Air New Zealand