RB25DET Series 1 & Series 2

[zoomswimmer]

I've been looking around and it is just confusing me more.
What is the difference between the Series 1 & Series 2 RB25DETs?
Some people said that the Series 1 is out of the R33
and the Series 2 is out of the R34?
Also other people have said that the series 1 and 2 are out of the R33 and the RB25DET with the neo head is completely different.
What is the RB25DET type 2? is it the same as the series 2? Some people this so, other think that they aren't. Some people haven't heard of it some think it is the neo, some do think that it exists.

Also, how much harder is it to install a NEO into a S13? I've heard that is it almost the same difficulty as the regular RB25DET, but the clutch is different (i think that it is a pull type instead of a push type) which makes it harder.

Thanks

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