Well..let me see...someone said the SBC was offered to Ford 1st when it was a totally in house project and they then attributed that information to a Mr. Smokey Yunick. Now I don't believe Smokey ever said that unless he was testing some reporter to see if the guy knew anything. Which he would do from time to time. And if the person who posted that on this forum knew anything at all about the SBC he would have know that Ed Cole was THE man on the project and was never employed as an engineer anywhere but GM. Around 45 years worth.
That was an unfortunate post; there was no "small block" formula that anyone owned and that he could shop it around from one manufacturer to another.
Anyway, as far as the primacy of the SBC, my understanding of the hot rod family tree is to begin with the '32 Ford V8 flattie. For nearly 20 years there was no other hot rod engine -- unless it was a Ford Model A four.
Next in the timeline I would put the Ardun heads for the flattie. Zora Arkus-Duntov did not invent overhead valves or hemi heads, but this product made them available (more or less) to the masses.
Next is the '49 ohv Cadillac and Oldsmobile (aka Rocket 88) ohv V8's. These were the first regular production ohv V8's. They provided the template for all the pushrod ohv V8's which followed.
Next is the '51 Chrysler hemi, which became the first mass-produced hi-po V8.
Next is the '55 small block Chevy, the first thin wall V8.
There should be another landmark for the big block V8. I would count the 1958 intro of the Ford FE as the first, although the big cube concept did not really kick in until the subsequent release of the 390's, 406's and 427's. There was also the Chrysler wedge-head "B" engine family, which replaced the hemi in '59, and which remained in production more than 20 years.
It took Chevy until '65 to catch up, with the 396 (although I believe there was also a very tiny run of '64 396 ci Malibus.) (I am counting only landmarks, and the Chevy 348/409 did not have the staying power to qualify as a landmark.)
And then there is the '65-'71 426 street hemi.
In other words, in the grand scheme of things the SBC is a landmark, but it is a crowded field. (I have left out many others.)
And the 302 Z/28 engine was the best small block carburated engine of the 1960's.
If the 302 was good, why wasn't the 365 hp 327 SBC better? It's the exact same recipe with 25 more cubes. And I don't believe anyone could argue the splayed valve heads on the Boss 302 didn't have more potential than the SBC's wedge head. In the '69 Trans Am the Boss 302 consistently enjoyed a 25-50 hp advantage over the SBC. In what sense was the Z/28 302 "better" than the 327/365 SBC or the Boss 302?