I've got a 90 hatcback SE 240SX with the complete stock SOHC engine.
Also have a 95 with the stock DOHC engine. I'm not sure if it's OBDI or II but IIRC it's OBDI because of reading somewhere that the o2 sensors/wires are different.
My question is if I wanted to install the DOHC engine to my s13, and if it happens to be OBDII, what kind of stuff would I have to deal with installing it? Same if it's OBDI. If it's OBDI I *think* I'd only need the harness and ecu.
I do plan on boosting on engine or the other.
Also how would I be 100% certain if it's OBDI or II. I remember pulling a code from the OBDII plug for my o2 sensor, but I think I remember the sensor before the pre-cat being a single wire sensor which if something I read is correct makes the engine OBDI.

Read that I could just hook it up by changing the sensors out if my car were a DOHC s13, but it's SOHC... Would I only have to get a harness and ecu from a dohc s13 and then change out the sensors and plug that into it and run perfectly?

YEAAH MAKE SURE CHANGE O2 SENSORS ALSO, VERY IMPORTANT

ALL S14s are OBDII compliant. Use the search to see how the swap is done. It's covered in multiple places.

Well, aside from one thing I have my 95's engine w/ auto ecu ready to go in and use my sohc transmission. I can't figure out what I should do about the inhibitor switch system. I'm obviously lacking the 3 plugs the writeup for an auto-manual swap show since my car is originally a manual anyway. What if I take my clutch safety switch's power wire and spliced it into the wire that goes to the inhibitor switch pin of the ecu, or even run my own wire to it?