I had a chance to develop the roll today and to cut a long story short nary a negative was to be found.
Bit sad but it was an interesting exercise.
I used Xtol for 12min at 20 degrees and although the fog was most certainly present, it was not overwhelming to the point where if there were negatives they would be unusable. Strangely though the fog was not even. Perhaps a mark of how the film was stored over the past 50 years...
Anyway, thank you all for your help and suggestions.