I’m curious about SBR engraving and interpreting the regs.

If you look at 479.102 (2) it says you can engrave the makers information on the barrel. As such, would there be any reason why you couldn’t engrave the upper receiver of the AR in a conspicuous manner?

The lower on an AR is the gun. That is where you must engrave.

The barrel is most certainly not a serialized component.

The only thing that has to be on the lower (the firearm) is the serial number.  If you're going to Form 1 an existing title 1 lower, that's already there.

The name and location for the maker can be added in all the places you quote from the CFR, and yes you could place that engraving on the barrel or upper if you wanted.

The reason most people don't put their name and location in those places is because barrels are wear items and will need replaced eventually, requiring another engraving.  Also, if you plan to have multiple short barrel uppers, engraving the upper/barrel would mean doing the engraving on all of those upper setups, so it's more work/investment in engraving.  It's easier to just put all the required engraving on the lower so you can freely swap uppers and barrels at will and remain compliant.

To my knowledge, it has never been clarified by the ATF if the "upper receiver" of an AR type firearm would be acceptable for the markings other than the serial number.

The barrel and serialized lower receiver are unambiguously acceptable.

The law defines the term "firearm frame or receiver" as "That part of a firearm which provides housing for the hammer, bolt or breechblock, and firing mechanism, and which is usually threaded at its forward portion to receive the barrel" (27 CFR § 478.11)

While either "receiver" of an AR type could meet that definition, the law is also generally precise in its wording that if it says "that part" then that means one and only one part can be considered the receiver under the legal definition. That being the case, the AR lower receiver has been defined as the "receiver" and I, personally, wouldn't want to be the test case for putting required markings on the AR upper receiver, if it ever came up.