well i am not 100% sure on this...
but you would need a new driveshaft, trany mounts to bolt up the transmission.. a calibrated tachometer and speedometer, according to the transmission... (and from what I have read on the SR20DE forums... swap the head from an DE to an VE) new oil feeds..
read this is guess... would help
SqUeEzE An Sr20Ve iNtO aN 240SX??? PoSsIbLe??