A. Yes, anything '84 and up in the tanks is directly interchangeable on a 700cc and larger Virago.
Comment: An on-line friend from way back has sent a suggestion on adding to this answer. I've missed his input!
Additional Information: 11-8-04 This just in from a long- time Virago nut, and someone I greatly respect!:
 
"While the 700/750/1000/1100 fuel tanks will physically interchange the 1000 and the 1100 have a reserve system that the 700 and 750ís do not.  Due to this reserve system the 1000 and 1100 tanks have two extra fittings located at the very rear bottom of the tank.  So, if you were to put a 750 tank on an 1100 there would be no way to connect the reserve fuel tank to the main tank due to the lack of these fittings or they would need to be added.  If an 1100 tank were used on a 750 the fittings would need to be plugged shut else fuel would run out the rear of the tank.  You may wish to note that the 84 and 85 700 and 1000 tanks are also slightly smaller in capacity and width then the tanks that were introduced on the 86 700 and 1100."