Give or take, around +/- 325000 of these were made in Japan and sold only in Australia & nz. RB30e S1 blocks were released in early VL Commodores by GMH, later in the production run VL used the only turbo version RB30et. Nissan did not release a turbo variation in the R31 or patrol. S2 blocks were 11 months or so later when Nissan released the RB30e in the R31 Skyline (JR31). Nissan later released a carby version for the GQ patrol, also S2 block.
Using Nissan nomenclature, RB30e & RB30et:
RB - engine designation
30 - capacity in litres
D = twin cam
E = electronic injection
T = turbo.
The RB30e is a single cam, electronic engine. It was never released as twin cam. To convert to twin cam there are a few small mods to perform, which is well documented.
To distinguish the differences between S1 and S2 blocks is actually quite easy.
All S2 blocks have the provisions machined to accept the turbo oil feed & return, & 1 coolant line at the back of the block.
Most but not all S2 blocks feature the front idler stud thread & pad for twin cam conversion machined on the front block face. Boost Doc sells a bolt on kit available to convert this on S1 blocks. The top idler stud has no provision, and this is drilled when the block is machined.
Most S1 blocks do not feature the twin cam idler pad, and they have blank pads (no threads or bolts) for the turbo lines (can easily be drilled by machine shop).
No turbo threads = S1 block.
By numbers, there are substantially many more S2 blocks compared to S1 blocks.
Everything else is the same.
There is nothing else different in the different versions of RB30 that will make or break a skyline build. The patrol blocks had an auxiliary M6 thread in the girdle to cater for the deep rear hump 4WD oil pan. The pick up tube uses this for mechanical support. Truly a nothing thing.
RB30et has an engine number designated as # A8 , where all other S2 blocks are Na blocks and are # A6. Apart from the 6 & 8, the blocks are identical in every aspect.
No RB30 uses oil squirters!
The quick and easy way to tell if a block is an RB30, well, it's stamped on it!! Both a casting and engine number! 2nd, there is extra metal between the deck height and the water pump, its very obvious when you study a 25/26 block and then a 30 block.