if your in ca then things might be different but a couple of my friends here in va who have sr's have gotten pulled over. sometimes the cops are dicks about it and sometimes they are cool about it. 1 cop actually pulled us over just so he could look under the hood. then he told my friend that he chose a good motor
the cops daily ride when he wasnt working was a turbo gsr. that cop was cool. then there was another cop who was just plain stupid. when my friend lifted the hood and the cop saw nissan on the valve cover, he didnt think twice about it. if the cop is in a really shitty mood then he can give you a ticket for it if he wants to and you will have to show up in court for it. the only way to get around that would be to remove the sr and put the ka back in for then. here in va if it's a small thing you get pulled for, like exhaust, and you have to show up in court, sometimes the judge will just ask for a pic of the old stock exhaust back on there. this might work for engines as well, but i doubt it. you should be fine with the sr. there are plenty here in the us already