One of those things I've noticed over the years, didn't think much of them, forgot completely, saw again, then forgot, and now I've looked a little deeper.
(I have nothing to do tonight and am bored!)
On one of the 77-78 Firebird front bumper assembly diagrams, but not all, there's a small twisted strap bracket referred to as Locator. It carries no part number, is not available to buyers, basically appears to have been an assembly tool. I figured it was perhaps used to hang the main bumper assembly from the centre with a hook while aligning the main brackets.
See part #3 - Locator.
Firebird 77-78 front bumper nosecone locator diagrams (2) by
Ben, on Flickr
Firebird 77-78 front bumper nosecone locator diagrams (1) by
Ben, on Flickr
On 79-81 models, they also have a Locator strap #8, but it stays on the assembly, #10008062.
79-81 Firebird front bumpor nosecone locator strap 10008062 by
Ben, on Flickr
79-81 Trans Am no nosecone by
Ben, on Flickr
Then I thought, maybe the 77-78 assembly was similar to 79-81, in that the strap from the nosecone mounted to something as well, just to align the parts. But for some reason it was also removed again, a shop tool for setting up. Be handy if it stayed in place for correct mounting angles and distance.
And yes, the 77-78 nosecone centre support also has a small hole just above the centre bumper hole.
77-78 Front bumper nosecone support by
Ben, on Flickr
Firebird 78 nosecone support bracket to bumper strap Locator holes (4) by
Ben, on Flickr
Firebird 78 nosecone support bracket to bumper strap Locator holes (3) by
Ben, on Flickr
Firebird 78 nosecone support bracket to bumper strap Locator holes (1) by
Ben, on Flickr
And just to confirm other trivial details, the 74-76 Assembly diagrams don't appear to use a Locator strap here. Their centre support bracket #527696 has no hole in place. For 77-78 they also used the same bracket, while it still carried the number #527696, it was revised. It still had the holes to mount the 74-76 top bracket if needed, but also had the lower hole added for the Locator strap on 77-78 models. It also has the locating dowel hole at the rear.
74-76 support.
74-78 Firebird nosecone support bracket 527696 with 74-76 small bracket (3) by
Ben, on Flickr
77-78 support.
76-78 Firebird nosecone centre support bracket 527696 (2) by
Ben, on Flickr
So there you go. Does it help in any way, afraid not.