Seeing as Callaghan was personally quite a popular PM, and Wilson would have been leader for 15 years in 1978, I can't see him doing much better against Thatcher out of personal charm. If he had chosen to pursue In Place of Strife or something like it, then that might boost his popularity enough to win an early election in 1978 (which he would be more likely to call as he already had a respectable amount of time as PM under his belt, unlike Callaghan), but the subsequent backlash from the Labour left and the trade union right would be very difficult for even a man of Wilsons talents to navigate. There is a chance he could beat Thatcher, but probably a smaller chance than Callaghan had in OTL.