LOL... I think the same dude installed my original AC set up, there were some seriously jagged hacked in holes in the firewall and at the core support they just bent a knockout section to route the hoses through. Not to mention the rubiks cube to remove or install any of the heat or AC components which were separate stand alone systems.
I welded up everything on the firewall (almost) and cut down the Vintage Air adapter plate so it would be flush. I would probably have custom made new mounting brackets that bolt on the inside of the firewall if I had to do it again, or maybe just weld some studs to the firewall to slip the unit over. It was an all day job mounting the VA box under the dash for the final time, even after test fitting it without the AC & heater lines several times. Laying upside down and backwards while holding the box in just the right position for the bolts to line up just ended up causing fights.
IIRC the welded nuts in the VA brackets had galled jacked up threads, I think we ended up drilling one of them out and using a slightly longer bolt and nut.
Also, it was a bit of a PIA to mount the new firewall pad without any of the holes for the rubber plugs to push through. You'll want to replace the pad before your final install if you plan on replacing it at all.
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