will a 95-98 ka24de fit in a 93 240sx and if so what do i need for the swap. if it is possible. thanks

Yes it will. As far as what you need, it depends on how you want to control it. If you are going to use the corresponding ECU, then just transfer all the same equipment from the new motor into your car. If you are going to use the S13 ECU, you need to swap the intake and exhaust manifolds fromt he S13 motor onto the S14 motor and use some of the equipment from the S13 motor as well. I don't have all the specifics. I just know this becuase someone I know did this swap.

If you're in cali, then swapping in all S14 motor and ECU would be beneficial since you can take it to a ref and have them sign it off as smog legal. Then any S14 parts with CARB E.O. numbers will be legal. Particularly the Greddy headers and even their turbo kit(if.when they ever finish it).

i have 120000mi on my 93 and i really don't want to try to build up the engine for it to break. So if i swap the 95-98 ka i will need the ecu and wiring harness? going with a turbocharger system would this be better or should i just rebuild my 93 ka? Thanks for any advice given.

personally, i'd rebuild. who's to say the newer engine was well maintained by the previous owner.