its always been kind of like the carbine vs rifle thing. Winchester has called 22inch 1886s carbines. Most would call that a rifle. Small block just means its the smaller block used in that line up of cars. Really to most of us theres only one small block and thats the first gen chevs. i rarely here a 289 ford or a 340 buick or a 340 mopar called a small block. more confusion? Ive seen people call buick 350s small blocks and there actually the same block that was used in the bigger motors so they would in fact be buick big blocks. This differnce gave the buick gs a substantial weight savings over a big block chev car. blurred even more today. We have storker small block chevs with as much displacement as big blocks in the 70s and even bigger blocked big blocks that push near a 1000 cubic in.
https://www.motortrend.com/how-to/1211sr-1005ci-godfather-big-block-engine/
now thats a big block. As much displacement in two cylinders as 90 percent of the cars on the road today have total.
you are correct to a degree in that the 348 and 409 Chevies were the same block but to over simplify, Pontiac up until the new block in the late seventies were same block different bore & stroke and Oldmobile were like AMC they just raised the deck height in the same block.
As I said that is a huge over simplification because on some makes part from early blocks absolutely will not work on later blocks due to design changes..
In the Fifties Chrysler had a lot of true small block Hemis that were unique to them selves.
The BUICK small block is not the same as the BUICK blig block in any way; the first one that replaced the BOP engine used the cylinder heads from the Buuick version of the BOP, on new block.
I did find out recently the first Iron Buick small block was the second lightest small block (discounting the BOP) produced by any one by tens of pounds; too bad back-door boys could not let Buick go raising, like Chevy, Olds and Pontiac did.
Before the last genuine Pontiac engine, the 301, which was a new block, Pontiac had first shaved , a lot, some blocks for Trans-Am racing before a small run of special shot deck blocks were made but then the Oil shortage killed the Trans-Am in it small block only form, racing so they were used by the short lived NASCAR pony car series.
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Sadly Sonny Leonard died about a year ago.
Even these huge mega blocks come in different deck heights from most engine block caster, from the original 9.8 of the first Chevy big-blocks up to 11.1 with some going higher than that.
The increase in bore spacing is where they really change from the original Chevy 4.84 to 5.00 to 5.20 and finally at 5.30; other makes now also have such a myriad of deck heights and bore spacing even some factory but to a huge degree in the after market.
