The interesting thing would be that Heath is liable to have held on until 1978/79 and would have had a much higher standing in the Conservative Party. This would have delayed Thatcher's advance and may have even delayed the spread of New Right attitudes even within the Conservative Party. Given he lived until 2005 (I had met him ten years earlier), there is a good chance he would have ended up as a long-term Prime Minister, perhaps well into the 1980s. As it was, Callaghan tacked towards the New Right even as a Labour Prime Minister from 1976, so it is unlikely with a continuing Heath government that these trends would be entirely absent from British politics. Still, I doubt Heath would have gone flat out, for example, to bring down the coal mining industry, despite the problems he had had with it.
Heath was much more of an internationalist than Thatcher and more pro-Europe rather than willing to become the USA's lapdog as Thatcher did in her relationship with Reagan. There would have been challenges, economically, with the winding down of old industries in Britain, but Heath is unlikely to have driven on with privatisation to the scale Thatcher did. He also tended to follow a policy of regional development/support. We are likely to have seen rifts in the Conservatives over Europe which were largely kept overshadowed under Thatcher but were to erupt under Major and beyond. Labour is likely to have followed a similar path with the radical vs. centrist divisions of the 1980s. However, without the seemingly very stark opponent in Thatcher, the more militant strands may not have received as much support as it did from dispirited members of our early 1980s.
I certainly think in that context it would have been Healey rather than Foot and there would have been a keener approach to Europe and certainly an avoidance of an advocating of unilateral nuclear disarmament. Though both major parties would have been sniped at from their extremes, it seems that the gap between Prime Minister Heath and Leader of the Opposition Healey would have been much narrower than between Thatcher and Foot/Kinnock and pro-Europeanism would have been the dominant tendency at the head of the parties, perhaps spawning Eurosceptic parties/pressure groups both from the right and the left.