It may be a bit unorthodox...
 

...but I want to put the VR4 engine, tranny, turbos, the whole works, in my '04 Neon. Is this possible? I read somewhere that the SOHC version of the 6g72 fits, so I figure with a bit of modification to the hood and top of the firewall, I should be able to squeeze the DOHC block in. I realize there will be need for a good deal of custom fabrication required (the exhaust, for example), but I am quite interested in pulling this off. If anyone has any information, I would be greatly appreciative.

the SOHC and DOHC are set-up completely different. Anything is possible, but it's a matter of just how much you want to spend.

Just the parts along, you're looking at roughly 4-5k, depending on specs, mileage, year, etc.

Then you're looking at a custom AWD conversion... NOT going to be easy on your car at all... since there is most likely no tunnel for the driveshaft to run, or enough space in the rear for a subframe and rear differential, etc.

You would basically need to tub out your entire car to fit the components you'll need, and even then, I don't think the neon is wide enough to fit the suspension/subframes for the VR4.

I don't want to rain on your parade, but you're probably going to be looking at a 30-40k build if you pay someone else to do it, and you'll end up with a heap of scrap metal if you try to do it yourself.

What are the differences between the SOHC and the DOHC, just so I understand the differences between the two motors?