Can i fit a 450c.i.d engine in my 2003 monte carlo and if so is there any Special things i need to change?

There is no room period for the transmission to even fit!!!!! You would have to have unlimited funds since it would be extremely high to attempt this, maybe buying a Ferrari would be cheaper. You would have to redo the floor in the center so you could actually tuck a transmission in there, you would have to redo the front to even get the engine to sit & modify the suspension, modify the rear to get an axle to even bolt up, by the time you were done modifying, it wouldnt even look like a Monte Carlo anymore. It would easier if you found something the body could be bolted to of a chassis that already has that engine in it!!!!!!! Than that way just modify the body mounting points & slap a Monte Carlo body onto the other chassis!!!!!!

Yes, you are messed up. And no, there is nothing special about the monte carlo so of course there is nothing special you need to change. Otherwise, go for it. $13,500 ought to do it. By the way, this is the GMC section. Isn't this monte carlo a Chevrolet? And then shouldn't this question be in the Chevrolet section? I mean, you post things in the wrong section you get wrong answers. Or did you not understand that this section exists because General Motors manufactured some vehicles which don't fit in Chevrolet or Pontiac?

You will need to change just about everything to put an 416 crate motor in there. You are better off just buying something else.