On an airplane you’re really paying for the engine. Typically after 2000 hours (depending on the model) they are supposed to be overhauled, which will be a cool $20-30k or so for something like the 172 in the OP. If you’re airplane shopping you’ll see a very tight correlation between the asking price and the “SMOH” time or hours since major overhaul.

For $20-30k, you likely can buy and install a new engine, or two, were it car engines. (That's the route taken in the article.)

Car or bike engines are not made to run continuously at 75% of max power with 1500-2000 between overhauls. Otherwise you can put a motorcycle engine in the plane, even better power to weight ratio (200 HP/liter) than car engines, but it does not work.

This article suggests that they started with a marine engine, typically an automotive engine that's been modified for these duty cycles by changing cams, timing, bearings, etc. Probably not all existing automotive engines are well suited to these applications, but they only need one or two.

Obviously an aviation application has other added constraints like elevation changes, inverted operation, packaging requirements, etc, but "runs at 75% max power for hours at a time" is certainly in common with the marine applications, and trivially demonstrated on a dyno stand.

GA does not fly inverted; elevation changes are influencing mostly the air mixture. Just saying, not contradicting.

Old marine applications would use carburetors and often those carburetors weren't at all suited to changes in elevation. (Most of my knowledge is actually only of a specific family of Volvo / Penta pushrod engines)

Probably airplanes, even in GA situations, are able to operate under negative Gs far more often that a typical marine application.... A person adapting such an engine would ideally think about oil pickup under such scenarios.

It seems like kind of a slam dunk, though I wonder about the reliability of a car engine left at full-throttle (or close to it) for long periods of time the way airplane engines are.

That’s part of the secret if you head over to the Corsair website: https://corsairpower.com/. They’ve significantly derated the engine with a custom ECU and added a gearbox to better match prop RPM to engine RPM. They’re rating it at “conservatively” (their words) 3000 hours TBO.