So much to unpack here!
First, clearly her 'joke' was that Sunak, far from being the uber-Thatcherite Chancellor, and Tory hero, Nigel Lawson of his own mind; was instead more of a Tony Barber - Heath's ill-fated Chancellor 1970-74 who lives in Tory/Thatcherite demonology for the Barber-boom and general failure (particularly over inflation) followed by two election defeats in a year (Feb and Oct 1974).
Second, this may be considered 'smart' by the sort of people who now run Labour - associating the current administration with the failed Heath government and the high inflation of the 1970s. And, bearing in mind their obsession with the pensioner vote, maybe even meaningful to anyone over the age of 60.
Third, as this was a dig that most Tory MPs would understand (particularly those of a certain age), it may have appealed to Reeves and her minders as just the kind of Parliamentary 'performance' that counts for the sort of people who think that politics is like an edition of the West Wing and part of the 'great game' at Westminster.
But of course the sad reality is that her 'joke' is completely meaningless for anyone who isn't a Parliamentary anorak, over the age of 50 or the sort of bizarre, and often sad, people who are attracted to Labour centrist politics. In the midst of the biggest cost of living crisis for decades, she offers us a bon mot about a Tory Prime Minister that left office 48 years ago and a Tory Chancellor who did the same 15 years later!
Meanwhile, the latest polls suggest more people trust the Tories with the economy than Labour, with 48% saying 'don't know' or 'neither'. Judged on this performance, who can blame them!
PS. Her abject performance (already inevitably lauded by the Guardian) brought to mind Denis Healey's famous retort to another Shadow Chancellor - 'like being savaged by a dead sheep.' Except that both Healey and his target (Geoffrey Howe) were genuinely men of stature who were quite capable of facing up to the great crises and issues of their time (whatever you may think about their politics or policies, and I opposed both).
PPS. I met Ted Heath once, but I was very pissed.