looks like its right before the airbox. it'll have a harness or something with a couple wires going to it. im assuming its MAF, i think a couple of the 3rd gen 5.0's had speed density, then they went back to maf. its no biggie, just find a k&n cone-type filter with a 3.5 or 4 inch opening. can use clamps to attach it to the MAF sensor. the sensor probably has 3 or 3.5 inch openings however so you wont see much of an improvement using bigger pipe than that. i dont recommend pvc either, aluminum is cheap, could have a muffler shop make you the piece, then polish the **** out of it on your own. it holds up to heat better, and the less turbulance you have before the intake the better. you'd have to use angled joints to do pvc, which would create turbulance, not to mention it'd just look ghetto.
or if you want to just get er done, just use the stock plastic piece there. remove the airbox, and put a new filter on your maf. best to have it as far away from the engine as possible though.
dont have any recent pics of my engine, i really need a digital camera. anyone want to donate or sell me one cheap?