Greg,
Giving this some thought after you called last nite, and your previous track record of using them on an older Wing, which IIRC was a bit heavier than the ZG, I would guess that the tires should work out ok......
Being the Spitfire's are belted, there's the Shinko 777 which I
CAN recommend & it's $81.99 here;
http://www.motorcycle-superstore.com/3/31/401/19716/ITEM/Shinko-777-Rear-Tire.aspxAlso, I mated it with the Shinko 011 Verge up front in the PROPER 120/70ZR-18 sizing & it worked very well...
http://www.motorcycle-superstore.com/1/28/394/28032/ITEM/Shinko-011-Verge-Radial-Front-Tire.aspxIf you want to match up belted f&r they have the 230 Shinko in the 110/90-18 sizing
http://www.motorcycle-superstore.com/1/28/395/6187/ITEM/Shinko-230-Tour-Master-Front-Tire.aspxThe last time I ordered from them, I had the tire in less than 3 days too!