67 SWB Bed floor questions - holes?

[pbmcauliffe]

I had this in the paint and body section, but hopefully will get some info in this section since it is a year specific deal.

As I satrted working on my 67 shortwide, I pulled up the bed mat the previous owner had in it and noticed A LOT of 1/8" holes in a pretty consistant pattern.
So here are the questions,
Was there some trim for the bed floor when it has a metal floor?
If a truck has a wood bed, isn't it open below the would except for the crossbrace?
Will the trim for a wood bed fit in the recesses of a metal floor and look okay?
Just trying to figure out what all the holes are for, and not looking forward to welding them all up if they aren't used for something