I created a WIKIBOOK about 240SX performance modification a while back, Here it is
It appears someone has written VQ series swap notes.
FWD, Comes out of a 95-01 Maxima. The Intake manifold will point towards the firewall, so modification will be necessary. The 00-01 Maxima with a VQ30DE-k has an improved intake manifold and a better power band. It is plastic and thus easier to modify. Tend to be found pretty cheap. 95-99: 190hp 205tq; 00-01: 222hp 217tq
RWD, Comes out of a JDM Cima or Cedric. Turbocharged version of the Maxima engine with stronger rods, pistons, and a beefier crank. The intake manifold is setup for RWD, but the stock turbo and header setup may require modification. Most have changed the setup before the swap. Uses the same sensors as the Maxima engine and but will require different tuning. Rare to find. 270hp 280tq
 FWD VQ35DE
Comes out of a 02+ Maxima, Altima, Murano, Quest, and others. Same long block as the RWD, but different motor mounts, oil pan, and intake manifold. Custom motor mounts are required as with the other FWD engines, but most other parts will swap directly over from the RWD VQ35s. Rated at around 255hp 265tq, but after the manifold swap and some modifications it will be the same as the RWD
 350Z and G35 VQ35DE
Includes the "Rev up" and regular 287hp DE from the 03-06 350Z and G35 engines. Very little modification to fit in. More expensive than the FWD versions. "regular": 287hp 274tq "Rev up": 300hp 260tq
07+ G35 Sedan or 350Z. Very rare and expensive. Uses a different transmission bolt pattern from the other VQ35s, but believed to be the same as the VQ40DE. Lots of top end. Revs to 7500. 306hp 268tq
05+ Pathfinder, Xterra, and Frontier. More rare and expensive than the VQ35 and believed to have a taller block. More low end torque based. Uses a different transmission bolt pattern from the VQ35s, but believed to be the same as the VQ35HR. 261hp 281tq
 Swap Guide
 Required Items
Engine - 350z, Maxima, Altima, G35
Tranny - 6 speed from the 350z, G35
ECU - 350z, Maxima, Altima, G35 or standalone (Many use the MegaSquirt II standalone or a stock VQ35 or Maxima VQ30 ECU). If using a nissan ECU you'll need the key, NATS module (mounts around the key cylinder) and ECU out of the same vehicle inorder for the ECU to let the car start - a securtity feature on most new Nissans (if you get them out of seperate vehicles you'll need to take your car to Nissan to have them program the ECU to the key) What all else will be necessary to run a stock Z/G ECU remains to be seen!
Radiator - I'm using the stock one.
Coolant pipe on back of heads - Z/G works best as it hugs the back of the motor tighter giving you better firewall clearance and puts the rad inlet on the RH side of the engine bay which works out muuuuch better.
Intake manifold - Z/G (all 3 pieces) for FWD VQ35, custom built or a modified Maxima/Altima unit
Exhaust manifolds - Z/G, the LH must be modified slightly to clear the steering shaft. This also depends on how low you mount the motor, the lower you put it the worse the clearance problem is. I had to hammer in the LH header about 1/4" or so.
Throttle body - depends mostly on what ECU your running and what intake manifold, I'm using a modified Z unit (converted to cable operation) on a Z manifold.
Motor mounts - custom like me if you're using a FWD motor, if using a RWD Z/G motor their motor mounts just might work as is.
Shifter - Z shifter on shortened Z linkage, as the shifter would normally be much farther back than the stock shifter.
Drive shaft - custom made consisting of a Z/G front yoke and your stock rear joint with a custom length tube. Either the 5AT front yoke or the 6MT front yoke will work, I'm using a 5AT unit.
Oil pan - RWD Z/G upper and Z/G/Maxima/Altima lower (metal pan) is necessary for crossmember clearance
Throttle position sensor - Depends again on what intake manifold, throttle body, and ECU you are using. I'm using a modified Z/G TPS
Tranny mount - stock 240 mount flipped 180 degrees with custom spacer made out of some hard rubber