If you have the original 327 in there, there are 3 oil pressure outlets. One, on the top/rear of the block, where you gauge fitting is now, and one on the front of the block, under where the oil filler tube is. There should also be one right above the oil filter.
If either of those alternates are not good, then you'll need to "tee" off of the rear block fitting where your gauge line is.
I saw your other post about mounting the pump, and the spare tire tub, but I didn't have any suggestions on that.
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Joel Adams
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