Well, another thing that's good about the skyline engine is that it provides more low down torque because of the bigger displacement. Also, you can fit a larger turbo on it and it won't be no where near as laggy as a 2L SR20.
But really, it's gonna cost so much to buy and install an RB26 in an s15. I really don't think it's worth it unless you have loads of cash to blow. Nonetheless, an RB26 s15 would fly!
How many people have skyline engines in an s15? And why did they do it?