Don't get us wrong, the XJ-S looks like a rather comfortable ride, and with the V12 is surely both smooth and powerful. It's just that Jags didn't have the best reputation for reliability back then, and we'd have been at least a little worried that we wouldn't make it all the way across France on this trip. Nor are we sure we would have wanted to without air conditioning.
The model in question, as you'll find out if you watch the video, is an early 1980 example, produced just before Jaguar updated the line with the High-Efficiency versions. As such, it's got a bit more power and shorter gearing than later models. The XJS (as it would later be labeled) would undergo a number of updates over the following years, and would stay on the market until 1996 when the XK came along to relieve it.
By Harry's reckoning, his early XJ-S was every bit as good as the Porsche 928 and other front-engined GTs of the era, and would have been more fondly remembered if it hadn't had to live in the shadow of the E-Type that came before. You'll want to watch the 17-minute video of the journey, undertaken for a cover story to appear in the September issue of Octane, to see for yourself.