I Installed a RB20DET in my Z this year and believe its a great way to go. It cetrainly doesnt have the grunt potential of the RB25 but its very affordable and is utlimately capable of putting a lot more power to the road than the L24..... at a lower cost.
And yes fuel consumption is pretty good, I cant tell you how much better as I dont really care but I know I can go further on a tank of gas. The comparison of a 2L to a 5L V8 is obvious.
They are reliable and most part are available through your friendly neighbourhood NISSAN dealer or eBay...or many other vendors!. I cant say how quick ta stock RB20 is compared to a stock Mustang as mine is not stock but its plently fast.... It doesnt need power steering. as it steers just like a stock L24 car.
As for the install.....pretty straight forward. You can buy engine mounts from various sources, fabricate your own tranny mount, buy an oil pan from NISSAN, build an exhaust, install an intercooler and wire it up. A bit simplified but pretty much on. and all the info is available right here on hybrdZ.
The one thing I dont like is that it seems to revs a bit slow for my liking.???.....I think this may be due to the heavy flywheel. So Im fixing that right now with a lightened one. Overall I, happy with the build.
Would I do it again or differently? Yes. I picked the RB20DET because it was 2L ( same as the 432Z), I wasnt looking for tons of HP, I wanted fuel economy, I wanted an easy car to drive and the RB20 cost less than all the other RBs. I would buy the RB25DET for the build paltform if I did it again. Do I regret my project?....not for an instant. Love it!