I am using my OEM Mustang GT Air Cannister as a homebrew Jeep CAI. The following pictures detail the components. I had to take a break from Jeep restoration the past two days to build a "tea cup" prop for my daughter's high school choral show. Anyway, I've based my build from the thread here that the guy used an Apollo CAI going thru the firewall into the cowl area. I will insert the rubber "horn" of the Stang unit thru the firewall. The inside diameter is about 3 1/2" which is more than adequate for air flow. More pics to follow when the install is complete. I would think this part would be easy to come by since it is usually the 1st bolt on performance item in the Mustang world.
This part below was $19.99 at Oreillys and is expandable/bendable. It answered any question/concern I had.
The stock air housing trimmed down to retain the PCV...
I had both a '94 & '96 Mustang and the '94/'95 style looks like it would make for an awkward looking modification. The Mass Air Flow sensor was mounted inside the airbox for the '94/'95 cars. There is a protrusion on the side of the air box would it look ugly. The '96+ cars have the MAF sensor external to the airbox.
The '96 Cobra shown there is the identical setup as my '04. That should be great news for availability. Not too many Stangs out there still have that original air can. Hopefully those guys saved them like me. As for the Mass Air Flow sensor, when unbolted and out of the way, the flexible hose I got from Oreilly's inserts from the inside and fits the hole very snug.
Weather permitting, I should be finished tonight. I drilled my hole through the firewall last night between rain showers but it is 3 1/8" and I need maybe another 1/8th on top/bottom. The rubber "horn" is very flexible but is not completely round. That part doesn't matter so much but the hole is just too small.
I have completed the modifications and installed the new homebrew CAI. I recommend using a 3 1/2" holesaw. I had to grind the bejesus out of the firewall since I used the 3 1/8" saw (what I had laying around). Because the "horn" is contoured and becomes larger as it approaches the filter, the larger the firewall hole, the closer the housing is to the firewall. That, by the way, is preferred to keep from interfering with the dipstick or oil fill. I still may tweak it some but I am very pleased.
The horn is rubber, stiff, and moderately flexible. You just cram it into the hole until it stops and its "in" for good. You really have to yank on it to get it out! I have not even permanently mounted the housing yet.
One word of advice: I removed the 3 factory attachment points. The housing is strong enough so that you can drill a hole in order to attach some sort of bracket if needed.