When the artisans stepped into the Sistine Chapel with brushes in hand in the early 1980s, onlookers fretted that despite a meticulously planned, desperately needed effort to restore the color and verve of Michelangelo's frescoes, they would ruin one of the world’s great cultural treasures.

So it goes with beloved works of art, something that anyone familiar with the Porsche 993 would agree includes that remarkable sports car. The third generation of Porsche's venerable 911, built from 1993 until 1998, is perhaps the best loved. It retains the classic shape of the 911, a miraculous engine, and sublime handling. It's not for nothing that Road & Track once called the 993 "something truly special." The car also induces wistfulness among Porsche aficionados, as it’s the last 911 with an air-cooled engine. All of which to say: This is not a car you want to ruin, or muck about with lightly.

That didn’t stop Peter Nam, whose custom car shop Guntherwerks just unveiled the 400R, a restoration and upgrade of the 993 designed to make the car more powerful, more modern, more ogle-worthy. “We basically gut the car down to the chassis,” Nam says.

Nam is the CEO of Vorsteiner, which builds things like body kits and wheels for performance cars, and he founded Guntherwerks specifically to remake the 993. Although Stuttgart produced a small number of the truly bonkers race-ready 993 GT2, they cost stupid amounts of money today. Nam wanted to bring that kind of cachet to some of the 70,000 or so 993s that Porsche built during the model's run.

“How great would it be to take the last air-cooled Porsche, the pinnacle of the 911,” Nam says, “and make it into what I would imagine as a GT3 RS as made by the factory?”

And to look at the result, revealed during the swirl of uber-swanky automotive events surrounding the Pebble Beach Concours d’Elegance, Nam wields his brush and palette well. The 400R retains the look and stance of the 993, but offers upgrades nearly everywhere.

The biggest change sits behind the rear axle. Gone is the coupe's original 3.6-liter boxer six, replaced by a 4.0-liter unit created just for this project. It makes more than 400 horsepower and 330 pound-feet of torque, with a 7,800-rpm redline, and still air cooled.

Nam replaced just about everything else, too. The 400R sports carbon fiber bodywork, made in-house. The LED headlights sit in 3D-printed housing made of carbon fiber, plastic, or handbrushed aluminum—your choice. The rear spoiler is new, as are the Bluetooth connection, satellite radio, and audio system. Of course the suspension bits, brakes, and wheels are bespoke to the 400R.

Guntherwerks isn’t the only shop doing this kind of work: Singer, in Los Angeles, specializes in revamping the second-generation 911, known as the 964. For something less reverent, take your Porsche to Magnus Walkerson’s shop and let him go wild.

But Nam’s effort seems to do everything possible to make its design stand out, with a focus on all the details. Every last detail. Even the key. “We didn’t want to reuse the original black plastic factory key,” Nam says. Instead, you get an aluminum key, in any color you like. It resides in a black felt-lined, walnut box, along with a custom-made fountain pen.

Of course, the remastered version of greatness has its price. For starters, you’ll need a Porsche 993 for Nam & Co to work on—Hemmings lists a few for around $50,000. Then, you’ll have to fork over at least $525,000 for the conversion, which takes four to five months. It’s a lot of dough, sure, but be wary of hesitation: Guntherwerks will only make 25 of them, and they’re likely to sell out faster than you can get the 400R to highway speed.