I think Callaghan and Jenkins are the most likely to take over from Wilson, though as Sunny Jim is the best unifier in the party besides Wilson, he'd probably be the better choice for Labour at that time.
Not too sure who'd be in a Callaghan cabinit.
If Callaghan is in charge, we can probably forget anything resembling 'In Place Of Strife'. When does Callaghan call the election? My guess is that given OTL 78/79, he'd wait until later 1970, or even delay until 1971.
If this happens and Jim and co get back in, does Heath resign? If so, who becomes Tory leader?