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The holes are in different locations. You can cut and patch to make it work. If I had to convert one, I would replace the firewall section with the one from the donor.
I'm not sure how different they are but that just might work. I'll have to see if I can get my brother to take a look too and see what he thinks. He's a mechanic by trade and a far better welder than I am.
Quote from: 79SierraGrande on April 15, 2015, 08:03:17 PMI'm not sure how different they are but that just might work. I'll have to see if I can get my brother to take a look too and see what he thinks. He's a mechanic by trade and a far better welder than I am. Welding in a portion of the firewall off the Suburban, as Sartobuilt said, is a good idea. Many years ago I converted a non/ac truck to factory a/c, but just cut and patched the areas necessary- I wish I had taken photos. The blower motor will physically be in the same location, so no cutting needed. Otherwise, on the non/ac cab, a portion of the firewall will need to be cut at the location of the evaporator and a portion of the firewall (over the area where the original heater core was located, adjacent to the evaporator hole) will need to covered. The patched and cut areas will be covered over by the a/c plenum under the hood and by the a/c ductwork inside the cab. Keep us updated and take lots of photos.
Here are pics from Sartobuilts firewall for AC for reference. If you have a donor you are ahead of the game to use the factory setup.http://forum.73-87chevytrucks.com/smforum/index.php?topic=21690.msg179454#msg179454
If you have a complete donor truck...it's a straight forward, nuts & bolts swap with the exception of drilling a few holes, closing a 1/8" dia. hole or Two & the mentioned 4" x 8" or so rectangle...which is the hole closest to the blower motor in the picture Capt. posted. Sartobuilts (the photos Capt. posted) was doing the opposite...going FROM A/C to non-A/C so he was closing off the inboard hole & cut the one you will be patching. There is NO need to cut any part of the donor firewall to weld in, unless you want to use it to cut that small rectangle out for your patch. The patch (all but a very little bit to the inboard side of the blower) is hidden by the new box, so it really doesn't have to be all that much...basically flat & sealed is what counts.What I've done is use a large piece of heavy paper/light cardboard & make a template (rub over the holes with a dirty finger & use a marker to locate the exact center of the holes) of the donor firewall. Go to your truck & match it up to the holes that match...some do. Hold the template in place with the existing screws & transfer the center of the new needed ones with a punch & drill. My Two Cents, Lorne