Chuck, did you fill those tires with helium?
I don't think so. "The Book" sez the Monza weighs 160kg dry. That translates to 352.7 lbs. Mine is bone stock and weighs 378.6.
The one that really surprised me was the Scura. I'm aware that Guzzis are all about lightness..
..but right around 500 lbs. is pretty good.