The SR number was stamped at the Pontiac Assembly plant. It corresponded to the red tag that was wire tied to the block. What I believe was the SR number was akin to a production block's Engine Serial Number. And the SR blocks were produced as an SR order arrived. So while no two SR blocks will have the same SR number, the SR number is only useful to Pontiac's internal paperwork at that time.
The SR blocks were the fitted block only (machined block, caps, pistons and wrist pins, etc). If whatever else was needed during a warranty claim or major failure repair was ordered separately.
The block itself was constructed of whatever production block was available at that time. So, for instance, a 67-70 RA block that was SR requested during the early 70s was constructed of a typical 481988 block that was machined for and fitted with 4-bolt main caps. The "481988" cast into the block was ground away and "9799915" was stamped into place.
There were single SR blocks that fit a wide array of applications. So most early 70s 455 SR blocks will have 4-bolt caps regardless of the application so it could fit the 4-bolt 455 HO or 2-barrel 455 with 2-bolt caps. Etc.
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