based on the article....
carbon fiber panels
metal supports drilled to swiss cheese, leaving only minimal structural stiffness
titanium exhaust
minimal interior
AC and heat removed
plastic and rubber bits removed
plexiglass windows
and of course... a "thin coating" of paint...
But seriously.. titanium exhaust and carbon fiber panels will save you a lot of weight... that's probably at least 200+lbs?
lightweight seats... and other interior bits... another 150lbs?
comfort parts removed (heat, AC) another 100lbs?
glass and all the rubber and plastic bits... another 100lbs.?
finally cutting and drilling out extra metal.
Depending on carbon fiber usage... if you replaced all panels, gas tank, roof, and other components with carbon fiber... that would be a lot of weight.