First thing I would do to the car is work on the suspension and brakes get that out of the way right now they are cheap upgrades. This gives you time to think about the motor. wether you want to keep the SOHC KA do a SR,RB,CA swap in it. Each motor has it advantages and disadvantages I have worked on all three and owned a S-13 which had 2 RB25's 2 Sr20's and a KA as well as other JDM S chassis cars. So feel free to ask any question. Also a Free note dose your seat hurt your back? you can fix that for free by unzipping the back and taking out the 3 springs that are for support you sit farther back and your back dose not hurt from driving.