Where can I find information on the rivets that hold or mount the Air Grabber (ducting) to the underside of the hood on a '69 GTX (440)?

I drilled the heads off of the originals from a '69 RR and counted I think 15+ STEEL large head rivets and would like to replace them with as close to original as possible. I bought some a few years ago from someone claiming them to be original but they are aluminum not steel and not sure they are remotely correct. Also I think they only sent me 10 or so, The original steel rivets also appear to have a flat head and not domed like what are available now in aluminum. The originals also being steel (and rusted ) I'm sure would not look like the bright aluminum rivets when new in '69, Almost considering going to McMaster-Carr and getting large head black aluminum rivets so they don't stick out like a sore thumb.

The dimensions and quantity of the originals would greatly help, thanks in advance.

Mike

..

I only counted 10 on mine - the outer boxes being screwed on.
One is asymetric, towards the front of the center ring.
Here's a couple of photos - unmolested 17,000-mile car.
Early Fox Mustang front bumper cover rivets are a dead ringer, AuVeCo probably still sells them.

I can do a recount if you like...