If it truly came from the factory with 8 Lug wheels it is very rare, 8 lug wheels came out sometime during the 1960 Model year, and from what I understand very few were purchased.
Without the PHS documentation it is hard to say if it actually came with them stock, but they could have been dealer installed or previous owner installed. A quick way we used to check if they were original is if the car has an 8 lug spare, and if it has the proper hold down plate. When a set is put on a car that didn't come with them (and I don't have a problem with that as they are a big upgrade in both braking performance and Looks) the spare and hold down plate seldom seem to be transfered