To answer your questions lets take a stab at it.
Mustang7302 - Havent really done much searching on the QR25DE and for some reason Nissan FWD dont mate well with RWD vehicles but amazingly a lot of the RWD motors mate perfectly to FWD application aint that some ****.
Sirsaechao - The dent isnt as bad as the picture makes it seem, but to fix it I will try to tap it out as best I can and prep the area with some bondo or some type of filler possibly lead? Anyone?
Scotty2Hotty2 - RB20DET are fun and nice motors, but unfortunatly little problems plague it such as overheating issues and Nissan messed up the wiring so theirs a bit of electrical problems. Also I cant justify putting a heavy *** motor with not much of a power gain. With the CA18DET which weighs 380lbs with tranny I shave off 200lbs from the stock 240sx setup and I get decent power. RB20, SR20 have around the same figures aboutb 200hp at the flywheel but the RB20 has a little bit more torque, now the CA18DET has 175hp and 168 ft/lbs of torque, with the SR T25 turbo I can achieve the same numbers as a SR20, RB20 hp wise while being a little more torquier than the SR20 all for $150. I'm pretty sure the RB motors weigh over 500lbs b/c the stock KA24DE weigh 520lbs with the tranny.
d1ck3r - the CA18DET is probably one of the best motors that nissan has ever created, the problems some people have encountered with CA's is actually just the turbo going out, or something stupid like human error like people trying to max out stock equipment like MAF, Injectors etc etc thats about it, you never hear about a CA blowing, etc etc also the CA was well designed that nissan actually took the same concept and technology and put it into their super motors for example the VG30DETT(300zx Twin Turbo and N/A Z32) has the same features and head design as the CA, the RB20DET, RB25DET, RB26DETT (Motors in Skylines) are pretty much super CA's, even the KA24DE shares some characteristics of the CA and a bit of the SR.
Thepbkid - Theirs a saying that goes around, you can do anything you want as long as you have the money. Their have been a few who have put VQ35DE(TT) to be honest dont get me wrong the VQ35DE is a sick *** motor but the cost to put one of those in is so much that for the same money could have a CA18DET doing 500whp with ease and redling at 10,000rpms. The VG30DE is fairly easy to put in because its a V6 so its 3 cylinders long as oppose to a I4, only thing about the VG30DE is that you need to make custom parts to make it fit b/c it just doesnt bolt in, also one thing to think about is weight the 240sx has a amazing weight balance I believe with the KA24DE it has a 52/48 weight balance and when I put the CA18DET in it will be around 50.1/49.9 not to mention the car will have gone from 2700 lb car to a sky under 2400 lb I did some weight reduction inside the car and in the engine bay.
mntbiker4life99 - if only life was that easy and money wasnt a problem. I cant justify spending $5000 on a motor, plus money to make custom parts or pay $1300 for custom brackets from Mckinney and converting the harness isnt as easy or cheap as well your looking at a easy $8000-$12,000 for the motor swap depending if you do most your work or if a shop does it. Also again RB motors arent light you might as well go with a LS1 you get about the same power as the RB26DETT but far lighter and its NA so no turbo lag, but then again you dont really feel lag on the RB26
And for some people who say just turbo a KA24DE, the CA18DET can handle 500hp on the stock block, its not recommended but their have been several incidents where people just slapped a bigger turbo, upgrading fuel delivery system, bigger injectors, standalone, and a really good tuner with a few dyno runs, its like the "little engine that could"