Well I have just dug out my photos of my old sunny with the L18 in it and looking thro them. I found a photo with the head of and it shows how tight the gearbox is to the top of the trans tunnel and also how close the block is to the fire wall. So as the RB 20 is a straight 6, I think that it could be done IF AND ONLY IF you want to spend lots of $$$$$$$$ to cut the hell out of the front of the car. But if you have LOTS OF $$$$$$$$$ then I think that $$$$$$$$ would be better spend on something else like a V6 or the like, just even for the fun of trying it!!!

So IF I had the money to do it and the time I would try it just for the fun of it to see if it could work!