There was a TL a while back which had it's PoD with Wilson standing down as Labour Leader in 1971 with Shore succeeding him. Whilst the overall premise was kinda iffy (Britain becomes American), it was still interesting enough.
However, I think that for Shore to get into a viable position to become Leader, you would need him to avoid being made Secretary of State for Economic Affairs, instead placing him into a role where Wilson can mold him as his protege without over-promoting him. Perhaps 1966 sees Labour do far better and win the lopsided victory it nearly did IoTL, with more people seeing Shore's Ideology as a winning ticket and thus having him gain a bigger base of support within and out of the Party. If Labour win a lopsided victory in 1966, then they are likely to stay in Goverment until the mid-seventies, with Wilson retiring either in 1972 or 1973. If Shore doesn't muck up, he'd be in a good position to succeed Wilson, and if there is an entry to the EEC Referendum, Shore would use a successful 'no' vote to catapult himself into Leadership and thus Premiership.