Introduced in 1963, the Chevelle was Chevrolet’s first venture in the then-emerging midsize car market. It remained the company’s bread-and-butter intermediate until it was phased out in 1977.

But the Chevelle was more than just a high-volume seller aimed at American families looking for something smaller than an Impala or Bel Air. Like most midsize vehicles that emerged in the 1960s, the Chevelle joined the muscle car wars by the end of the decade.

It all started in mid-1965 with the arrival of the Z-16, but the transformation became complete in 1969. That’s when Chevrolet gave the Chevelle a more aggressive appearance and introduced a beefed-up 454-cubic-inch (7.4-liter) big-block V8.

Called the LS6 and rated at 450 horsepower, the 454 V8 turned the Chevelle into the most potent US production vehicle at the time. It delivered 25 horsepower more than any HEMI-equipped Chrysler, while Ford’s Cobra Jet mill was no match for it at 375 horses.

The 454 LS6 wasn’t the only potent V8 lump available in the Chevelle then. Chevrolet also offered an LS5 version. The SS 396 variant was no slouch either, thanks to a 402-cubic-inch (6.6-liter) V8 good for 350 or 375 horsepower.

The Chevelle SS you see here is not a 454 or even a top-tier 396, but it’s pretty special for several reasons. For starters, it’s an unrestored survivor that’s still in one piece some 53 years after it left the assembly line.

It’s not the kind of classic I would describe as all-original, but it comes close. While some features have been altered over the years, the hardtop retains most of its original components. The list includes the 350-horsepower V8 engine, even though the mill is not currently under the hood.

This Chevelle draws juice from a 502-cubic-inch (8.2-liter) crate engine as of this writing, but the original 402 big-block still exists. It’s a partially rebuilt unit on a stand waiting to get the final touches before it finds its way back into the car. And it’s much spicier than before, thanks to a few high-performance internals that reportedly increased output to around 500 horsepower. Yup, that’s more than even the rare and desirable SS 454 LS6.

And that’s not all. This Chevelle also rocks a rare color combo. Sure, the Medium Green (also known as Mist Green) finish is not exactly scarce, but this hardtop comes with a matching interior and a dark green vinyl top. The latter makes the combo rare because many Mist Green cars were ordered with black or no vinyl tops. Oh, and it also comes with a front bench seat instead of the more common and SS-specific buckets.

Finally, the car’s previous owner was Grady Martin, Willie Nelson’s studio guitarist in the late 1960s and early 1970s. Granted, it wasn’t owned by Nelson himself, but it’s still a cool link to one of America’s greatest country musicians.

So what’s the deal with this Chevelle? Well, it spent many years in storage until it was discovered by 1970 Chevelle SS expert Patrick Glenn Nichols. He purchased the car and plans to return it to the road with the original engine. It’s a decidedly cool find since unrestored 1970 Chevelles that are still in one piece after 50 years are a rare sight. Check it out in the video below.