Hammered...Here's what I measured for the seat belt holders. First off there are 2 holes, one for the small phillips head srew and the second for the small tab on the backside of the holder. All meaurements will be to center of hole openings. If you measure your front console bracket mounting hole it will be 3/4" down from top of console. The top hole for the holder is also down 3/4". The distance between these 2 holes is 8". The lower hole for the holder is 1 5/8" down from top of console and distance between the 2 holder holes 1/2".
I'm sure the repro seat belt holders are available form the Firebird catalogs but in the Rick's Camaro catalog they are listed for $13.95 pair and it says they are triple chrome plated. I'll be buying some myself.
There's a guy on ebay that sells the mirrors for the sunvisors if you decide to use your sunvisors. He is the one who redid my sunvisors from the extra material I got with a new headliner, he does excellent work.