I think most pulley that are bigger than 4 or bigger are silver.
Measure it

stock 7.5
2lb 8
4lb 8.5
6lb 9
8lb 9.5

These are just rough numbers

 

Since you seem to have a bunch of mods and are curious to find out, I would try finding some vehicle history and asking the original owner themselves.

Also it might be chipped.

Check under the dash on the passenger side (above the fuel cutoff on the right) to see if the computer has a piggyback chip on it.

 

Ok thanks, I am about to go outside and check, I had wanted to check but didn't know where the chip/computer would be. There was a dyno sheet from team ford of marietta in the glove box that had 375hp/475'#'s but I don't know if it still sits the way it did when it was dyno'd.