It does stick about half way into the fender well. The opening in the engine bay to the fender well is not very big and won't allow for a very big filter. The roofing flashing is there to make it look clean, and to separate the hot air from the cold air as much as possible.

 

Just having less surface area will pull in less air and actually hurt performance, if the filter is as small as it looks in the picture

You can mail order ABS anywhere online, now that you know the demensions from your PVC