I went to high school with a kid who had a RB25 in a S14 (graduated from Tabb). It took him a while to get everything together and put in, but its possible. It really all depends on how much you want to make, what you want to do with it, and how dedicated you are to the swap. Also keep in mind that it will be a bit harder to find parts without having to order them. I mean I've seen a SR swap that took 2 days, and been party to a B series swap that took a little over 18 hours. It would have gone faster if we didn't stop to get drunk.