Disregarding the structural considerations, I would suggest that any aeroplane without an inverted fuel/oil system is not designed for intentional, sustained negative G. Now taking into account the structural considerations, the pilot would be wise to fly to reduced G limits rather than those published when the Chippy was a shiny new aeroplane. After all, fifty years of aeros is going to cause cracks and fatigue.
A chippy can do very nice aeros without exceeding 0/+4G, so why push it further? After all you would do handbrake turns and doughnuts in Bentley Blower would you?