YOU WILL NOT BE ABLE TO LAY THOSE WITHOUT CUSTOM ARMS AS FAR AS I KNOW.... I WOULD LOOK INTO GETTING 30 SERIES RUBBER... THAT SHOULD SET YOU ON THE GROUND.. THE MAX DIAMETER I CAN LAY OUT ON IS 24 1/2" HERE IS THE WEBSITE I USE TO GET DIMENSIONS
http://www.miata.net/garage/tirecalc.html PLEASE NOTE THAT THE DEFAULT "STOCK TIRE SIZE" IS FOR A MIATA NOT A B SERIES
HOPE THIS HELPS