Turning a convertible into a coupe is much more difficult than turning a coupe into a convertible, but the results are usually worth it. In 1963, Standard-Triumph’s engineers sent a Spitfire convertible, then hardly a year into production, to longtime Triumph booster Giovanni Michelotti. The Italian designer returned with a dramatic fastback design, long and sleek and nearly Porsche-like, one that only improved with age.

It is a stunning, swooping affair, a rare sight anywhere. It was cheap, too, relatively speaking: inevitable and hackneyed “poor man’s Jaguar E-Type” comparisons are still being touted today.

When the prototypes were built, the coupe’s extra weight added so much power that the four-cylinder Spitfire engine could hardly move out of its own way. In most British cars, that seems to be the norm. But for the GT6, a car that actually looks like it could be quick, that just wouldn’t do—so in went the 2.0-liter inline-six from the 2000 sedan, and the necessitating “power budge” that went with it. All cars deserve the “power bulge.” And few things in life seem more proper than a coupe with a Big Six up front.

Triumph always claimed that the GT6 was derived from the Le Mans-fighting Spitfire program, but that’s just marketing hyperbole. Michelotti began penning the GT6 in 1963, and the separate attack on the 24 Hours of Le Mans began in earnest a year later. In 1965, a Spitfire won its class. And when the Spitfire race car switched to coupe guise, it had some good groundwork laid before it.

Triumph may have built over 300,000 Spitfires in a little under two decades—but the company churned out just 40,926 GT6s.

The final major facelift for the GT6 came in 1970 in the form of the Mk III. This time the entire bodyshell was revised to match the changes made to the Spitfire Mk IV: modifications included a cut-off rear end, recessed door handles and a smoother front end. Only detail changes were made to the mechanics, but in 1973 – close to the end of the car’s production life – the rear suspension was changed again, this time for the cheaper (but still effective) “swing-spring” layout fitted to the Spitfire Mk IV. This was a modification of the swing axle rear suspension used on the Herald-derived models, with the transverse leaf spring mounted on a pivot, eliminating roll stiffness at the rear, and thus greatly reducing the jacking effect under cornering loads. To compensate for this loss of roll stiffness, a larger front anti-roll bar was fitted. A brake servo was also added in 1973, and seats were changed from vinyl to cloth. There was still a fairly comprehensive options list, but the knock-on wire wheels were no longer available. The unladen weight increased slightly to 2,030 lb (920 kg).

Engine power and torque for the Mk III was similar to the Mk II, but better aerodynamics led to a new top speed of 112 mph (180 km/h) and a 0–60 mph (0–97 km/h) time of 10.1 seconds. The last USA models performed relatively poorly, owing to the compression ratios being reduced to allow the use of lower octane unleaded gasoline.

The Mk III never sold in the numbers hoped for by Triumph, and was comprehensively beaten in the marketplace by the MGB. Triumph refused to release an official convertible version of the GT6 and, after poor sales, it was dropped from the Triumph range at the end of 1973, although a few cars were sold the following year.

“Driving a GT6 is an absolute blast,” writes Hemmings. “If you like luxury, refinement and a feeling of solidity in an automobile, this isn’t the car for you. But if you enjoy the responsive nimbleness of a short-wheelbase two-seater that can quickly go from slight understeer to oversteer in the blink of an eye, then this is the sports car you’ve long been waiting for.”