If it was a decisive majority win for the Conservatives in '74, we'd probably see Wilson resign as Labour leader. The question of who would be the next party leader is probably a toss-up between Callaghan or Foot, if we were to follow through to the OTL 1976 Labour leadership election. I'm not sure how it would have gone in terms of the leadership - if Callaghan can prevent other members of the right-wing from standing he is probably the favourite, though Foot might be able to pull it off.
The big question would be how could Heath have pulled for the win, which would help to determine how this 1970s would continue. If nothing else, the One Nation Conservatism that Heath followed might be killed deader with all of the Troubles, the Winter of Discontent, etc. so we'd see a more aggressive take to monetarism possibly during his premiership. That would probably result in a bigger economic downturn so that by the next GE, it would either be a hung parliament with Labour as the largest party or a Labour majority outright.