On the subject of pistons hitting valves, they only time I have heard of this was with a 1071 Cooper 'S' which had a 649 cam, 1,5 rockers and over 11:1 CR. With a 1071 the chamber volumes would be small and this the distance from piston top tos valve heads would be small. It would be even less with a 970.
Whilst competing the driver missed a gear on change up and the engine revved to 'a high figure' (maybe 8500+) and one of the valves stayed open due to the valve bounce 'kissed' a piston. The piston was fine and the valve was changed.
A road Mini is unlikely to fact this issue.
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