I think the starting premise of this thread is wrong on two counts: Heath winning in '74 doesn't offer a very satisfactory point of divergence away from the post-war consensus in either party.
Heath winning a majority and then being deposed Because Reasons is... odd. Now, expectations management was poor going into that election, and a lot of neutral media types thought, a bit similar to 2017, that we were headed for a big fat Tory majority; but if Heath actually returns with
a majority, he's going to be okay for the remainder of the parliament. Quite apart from the mechanism not actually being there to depose a Tory leader, even in the more permissive environment in the decades since it's a hard, hard thing to outright depose a PM. Mrs T, after all, got chucked on essentially a technicality of the rules, not on losing per se.
A political point, perhaps, but I think that parliament is better for Heath on a majority than Wilson's OTL fag-end government. The Industrial Relations Act, probably in a modified form, and prices and incomes continuing, and the government having more room for manoeuvre on inflation than Labour had, that likely means no IMF; but Heath's boom and the global situation, those are big drag factors.
No mythology around the unions bringing down the gubmint, that's a pretty huge divergence away from Thatcherism.
Equally, in Labour, you're dealing with a situation which is much less fraught than five years later in OTL. Five years less of the left growth we got after 1970; and I think without his loyalist Cabinet minister experience, Foot is either unviable or at least not the favourite in the subsequent leadership election. Most likely it's Callaghan. Benn? Forget it.
I'm surprised that there's not any kind of context here around Benn's AES being in reaction to a crisis of
Labour as a social democratic force, not any kind of reaction to the right. That doesn't happen ITTL. He's still going to be arguing for command economics etc, but the autarkic weirdness, that's not really going to be an issue without Labour presiding over the
county under siege from global capital IMF loan.
And I think that's the route down the boulevard people want here; Just as the failure of the 1970-1974 gubmint was a formative thing in the Tories, I think that the more exposure Labour has in government during economic crisis offers the most potential for some kind of big Labour break with the post-war consensus.
Labour being in power for the entirety of a much more crunchy seventies, that's maybe the route here.
I agree with what you said about there needing to be a wider shift elsewhere - one of the massive props to Thatcherism IOTL was the presence of Reagan doing Very Similar Things in America which made everything she was doing seem sensible,
I don't think this is true, and I think the goals involved, the focuses, were actually pretty different.
The big first term move and one of the biggest, most experimental - and IMO, worst - aspects of the Thatcher gubmint, though it's elided in mythology today, namely the 1981 budget, that's completely independent of the Gipper's neophyte administration.
Just as in OTL with Healey-period Labour, there was in any case the beginnings of a mood-shift in the Dems; Carter ran a very moderate, deregulating administration; and Jerry in California had, after a tax revolt, taken up the mantle of being a tax-cutter.
There's a chance that if Ford had won in 1976, a Dem who wins in 1980 is either a full-blown Down Under-style neoliberal type, and at minimum, they're going to be heavily pressured by that tendency.