The level crossing you're describing was on the WCML, but George's grandad's was on the Blisworth - Peterborough line where it crossed the old Banbury Lane and was called 'Rothersthorpe Road Crossing'. It was Northampton side of Rothersthorpe and was where there's an S bend just before the canal bridge ( Northampton branch of GU canal) coming out of town. Confusingly there another canal bridge ( main GU canal) next to 'your' Banbury Lane crossing where incidentally I used to spot in the 50s. ( Coros, Scots, Pats and Jubs were the main fare then). George's grandad's crossing disappeared in the 60s I think, although part of the line leading towards it survived longer as some sort of test facility for track maintainance. There's a picture of a Class 40 crossing it in 'Steam Images around Northamptonshire' on the same page as another one of 'your' Banbury Lane crossing.
George - yes it was Banbury Lane - went there myself to spot many a time when living at home watching the 80 series electrics whizz past. Also went in the box a few times as Dad knew the Signalman. Great times - it didn't half move when the trains hurtled through
It can get really confusing can't it?