[HO455]

There are 5 different kinds of fasteners (Not counting some of the odd ones that the truck has collected over the years) used to hold the wood down. (Photo 1) Bolts #2 & 3 are used to bolt the spare tire wheel well in.
In addition GM used two kinds of nuts on the bottom, a regular hex style requiring a 1/2" wrench to remove and square stove bolt style nuts that require a 7/16" 8 point socket for removal.
Bolt #4 is used around the perimeter of the wood and is the most numerous. I don't have a count yet but, I will get a complete list posted.
Bolt #1 is used to fasten the wood to the underside support channels that run from one side of the truck to the other. They don't connect to the frame. These are a carriage style bolt with a large flat head. These bolts are counter sunk below the level of the floor and have a little metal insert under the head of the bolt with a square hole to match the square under the head of bolt. (See photos 2 & 3) I do not know if the metal inserts with the square hole are available so I am hoping that I can reuse all of them.
Bolt #5 is used to secure the floor across the back. (Last photos) They go through a light guage angle with stamped countersunk holes with square holes. These bolts are called Plow Head bolts and as far as I know they are not available in the size used on our Burban.

There are 12 of the #1 bolt.
There are 7 of the #2 bolt ( I think, I can't read my handwriting. Dhoo!)
There are 6 of the #3 bolt
There are 39 or 40 of the #4 bolt. Mine had 39 but there was a punched hole in the driver's side wheel well that appears to never had a bolt installed.
There are 6 of the #5 bolt.