The all-aluminum big-block engine known as the ZL-1 is perhaps the unicorn of late-60s General Motors engineering. The engine, displacing 427 cubic inches and rated at 430 gross horsepower, saw only 69 copies produced in the 1969 model year–and here’s one of them up for grabs on eBay right now–for the tidy sum of $49,995.

Each ZL-1 engine was hand-assembled in a process that reportedly took 16 hours at the Tonawanda Assembly Plant, and with exhaust modifications and other tuning, were able to crank out over 500 horsepower from the factory-built mill – a huge accomplishment for the era.

According to the seller, the engine is currently installed in the #40 ZL-1 Camaro, and the only reason for its auction is that the original engine from the car has been located and is currently undergoing a restoration, leaving this particular ZL-1 up for sale.

The block is dated May 1969, and the seller says it had no repairs or damage and has never been blown up–no small feat for an engine that was originally designed for drag racing.

The engine has been rebuilt, however, and new old stock parts were used throughout, including the camshaft, piddle valve lifters, valvetrain components, connecting rods, balancer, and more. An original intake manifold was also located to finish off the build.

It’s not too often we see one of these come up for auction, and the selling price reflects the rarity of such. Even so, purchasing this bad boy for the Buy It Now price will likely get you roughly two-thirds of the way to an all-new 2016 ZL-1 when they are released next year. Guess it all depends on whether you’re into old-school or new muscle.

We’d take the warranty.