The OEM replacement engine sold by GM was called "Target Master". They're new, not rebuilt engines, available in a variety of horsepower ranges and options, from basic stock replacement types to some pretty impressive high performance numbers. For instance, the 502 cubic inch big block is available only as a parts department option, never installed as original equipment in any vehicle. It was originally offered as an upgrade for motorhomes, but the hotrodders have sort of taken it over as an over-the-top option for street rods.
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!