How often do cambelts fail "in general experience", providing they are replaced at the recommended interval and correctly tensioned including re-tensioning after the recommended settling in mileage?
And how many of those failures incur damage due to interference?
I have taken the view re redblocks not to worry on the interference issue, just make sure the cambelt is changed and tensioned. Cushti. And one can't guard against absolutely everything.
In general experience, that is a lovely can of worms dangling from a piece of string. 
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