Thanks.
Digging into this is confusing, as ever... The cars are referred to as either M6GT or M6BGT in nearly all places. Bonhams referred to it as M6 GT but auction companies consistently get it wrong and that was no exception.
Here are a couple of articles about the history of the car:
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Bruce McLaren’s dream: The McLaren M6BGT
Bruce McLaren’s vision was not only to dominate the worlds of Formula 1 and CanAm racing on tracks all over the globe, but also to produce some extra-special McLaren machinery for the roads.
His first foray into this brave new world was the stunning McLaren M6BGT, a GT car for road use, of which only two prototypes were made, before Bruce’s tragic and untimely death at Goodwood in 1970.
Had he lived longer, it’s almost a foregone conclusion that we would have seen more Bruce McLaren masterclasses in automotive machinery before long. Sadly, the M6BGT is the only road-going Bruce McLaren-built legacy left behind, but it is a truly stunning one.
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McLaren's Early Plans for a Road Car Bearing His Name
A road car bearing the name "McLaren" was an ambition that became a five-year off and on project, that was to be achieved once the company was well under way. The first inkling that Bruce McLaren indeed had the more sporting motorist in mind appeared in the racing press in the mid-1968, when it was rumoured that consideration was being given to the homologation of a coupe version of the McLaren-Elva sports racing car to compete with the Lola T70 in Group 4. The M6A had proven eminently successful in the Can-Am Series, so what better test-bed by which to assess the merits of the venture than the production-line M6B? The Kiwi maestro had fond hopes of thrashing it out with Porsche, Ferrari, and Alfa, on the circuits of Europe, and, besides, what was wrong with importing the old American "win-on-Sunday-sell-on-Monday" philosophy? It was some time before his dream was to become a reality. Revised rules for the F1A Group 5 World Championship for Makes had been altered to require a minimum of 50 identical models before homologation. And they had to be complete cars, unlike McLaren’s plans for the M6BGT which left the engine option to the customer. The longed-for homologation papers were, therefore, never to materialise, and the project started to die a slow death.
Later Developments
Early in 1970, however, McLaren had a prototype prepared using one of 50 all-enveloping bodies (which had been delivered for homologation purposes) to surround a stock M6B chassis. It soon became his favourite project, and, amid speculation over an unusual vehicle making a hash of traffic in and around Walton-on-Thames, Trojan Cars released the news that they had in fact cobbled up a road-trimmed version "for evaluation purposes, as it is possible that Trojan may market a road-going version of the M6BGT".
In his book, McLaren! The Man, The Cars & The Team, Eion Young reveals McLaren’s thoughts at the time: "Building his own road car was a project that had interested Bruce as an ambition to be achieved when the company was well under way with the racing programme".
But such high hopes soon gave way to disaster when the personable New Zealander met his tragic and untimely end on June 2 while testing the new model M8D Can-Am car at Goodwood.
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As you might deduce from this, I'm not entirely in agreement that the 'M6' part of the car's name can be extracted and used in isolation! As I said before, you could continue from 'Jaguar' with a car beginning with 'G', on the basis there's a 'G' in 'Jaguar'!