Just out of curiosity, what's the serial number on your z body?
I've got an STO that's a bit of a mystery. It's a 2k1 model, with a pre99 embossed serial number style, and a unique type of banjo bolt threading that's neither pre nor post 2000.
I heard a rumor that said the Orr's would use/sell batches of, not necessarily seconds, but perhaps excess stock, as prototypes/pl's. I've heard my STO falls into being a pre production prototype as a friends and family christmas gift of sorts.
Hopefully someone will see this and actually know what's up with the wonky frontblock threads.