Okay here are a few photos - not entirely sure this is what you are after. Also my garage is a little dark so I will try to reference and explain under each photo the best I can:
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So here is an illustration out of the 68 factory service manual of what I think you are talking about.
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This is looking down between my grill and a/c condenser. The dark red bar coming down and curving under the ac condenser is the center bracket. It bolts into frame crossmember. About halfway down you will see a bracket that comes off this center bracket horizontally and bolts into a lip on the lower valence.
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Another pic of the center bracket curving under the ac condenser.
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Slightly different pic angle showing one of the bolts. Should be two more bolts just to the right of this bolt by the FSM illustration,
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Pic showing a closer shot of the horizontal bracket coming off the center bracket.
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Probably confusing but this one handed hail mary iphone pic was taken from the bottom of the car pointing up and shows where the horizontal bracket attached to a lip on the valence.
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Looking down to show where the horizontal bracket is supposed to be attached to the valence lip. As you can see on my 68 the hole on the bracket does not line up to the lip hole and it is not attached! Not sure why, I did get into an accident many moons ago in a snowstorm in northern Arizona, but do not recall if that area was damaged or not. Anyway, something to fix in my fix up project!
Hope these pics help. Scott