McLaren makes its own cars, right? Sure, it does today – supercars, in fact – but that wasn’t always the case. There was the SLR that it made in all its numerous iterations for then-partner Mercedes-Benz between 2003 and 2010.

But there was also a Mustang it extensively modified way back in the 1980s.

Hold on, a Ford Mustang, modified by McLaren? That’s right. Way back, about a decade before it hit the road with the legendary McLaren F1, the British racing team produced a special version of the Blue Oval pony car. And there’s one of the original prototypes up for grabs on BringATrailer.

Woking’s take on the Mustang was based on the Malaise-era, Fox-body Mustang, and though it featured extensive modifications, it hardly produced what you’d think of as McLaren levels of output and performance. Instead of the big 5.0-liter V8 (and long before the modern EcoBoost engine), the 1980 Ford Mustang McLaren M-81 packed a 2.3-liter turbo four with variable boost sending all of 175 horsepower to the rear wheels though a four-speed manual.

It also featured extensive upgrades to the bodywork, interior, suspension, and rolling stock – capped by BBS alloys measuring all of 15 inches in diameter. The result of all those modifications was a 0-60 time clocked by Motor Trend at 9.76 seconds. In that same span of time, today’s McLaren 650S would have already be running at over 130 miles per hour.

Little wonder, then, that despite plans to make over 249 examples, only ten were produced. (A later version made in partnership with the American Sunroof Company would yield a larger production run.) This cherry of an example is decked out in McLaren’s signature shade of papaya orange, and has less than 5,000 miles on the odometer.

As we write these words, bidding is up to $20,500, with four days left to go, after a previous auction on the same site fell through at $36,250. That may seem like a lot when you consider that it originally sold for $25,000 when new. But that was back in 1980 when a Porsche 911 cost little over $30,000. By today’s standards, with inflation taken into account, the McLaren Mustang’s list price would work out to over $70,000 – which is more than you’d have to pay today for a top-of-the-line Shelby GT350R, but about a third of the MSRP on a new entry-level McLaren 570S.

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