I did air grabber on my factory ac car that got changed to a classic air set up. i put it in almost the spot as the factory which your almost forced to due to cable length but raised it up about 3/8" to clear the heater box if i remember correct theres a small dimple in the firewall where the factory hole would be.
after looking at the pics I must of moved it to the left & not up
here's some pics of the parts car that I swiped some parts & measurements from but if you look closely they should give you some good reference points but I strongly suggest drilling a pilot hole first since you don't have any room for error than I just used a step drill bit to finish drill the hole which gave me the perfect diameter for the grommet.
the other pics are of my car completed sorry I don't have any better photos but if you zoom in & follow the cable you can see where it goes in the firewall.
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