Hard seats for unleaded gas is a myth that was pretty much debunked a couple of decades ago or more, but the story still persists for some reason. Remember the phrase "old wives' tales"? When something like that gets repeated about cars, I call them "Old mehanics' tales". "Keep a hot engine running while adding water" is one of the classics. If you're driving a Model T Ford or maybe a Farmall Cub tractor (engines that don't have a water pump) that advice might have been sort of correct. In reality, the way to add water to a hot engine is to shut it down and wait until it's a cold engine! Running it simply forces the cold water into the engine faster, where it can crack cylinder walls, or cause a steam eruption that will injure someone.

Hardened valve seats are only necessary for engines running a "dry" fuel like Propane or LP gas, or maybe ones that spend a long time running against a heavy load at wide open throttle. Hobby restorations like the average stovebolt engine powers just don't qualify on either situation, and the process of counterboring a decades-old cylinder head for hard seats and pounding them into place with a heavy hammer and a seat driver is a pretty risky procedure. Too loose of a counterbore, and the seat can fall out, and if it's too tight the head can be cracked during the installation procedure. All for an imaginary benefit!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!