I happen to know Bill reasonably well - he was a 463 Sqn skipper. I was having a look through the 463 Sqn operational records a couple of months ago and saw that Bill came back with an 'aiming point' photo from each of his first three trips. When I mentioned that to him he promptly sent me a copy of one of them, from a Munich raid on 24 April 1944. The original is still in his logbook.
He apologied that he would not be at the annual lunch on ANZAC Day this year... when he explained why - the Tiger Moth - I thought that was one of the better excuses I've heard!! There's some footage in an ABC report here:
Veteran WWII pilot Bill Purdy still flying Tiger Moths at 90 - ABC News (Australian Broadcasting Corporation)
Fit as a fiddle and still holds a current PPL. Quite a bloke!
Adam