Re: fuel tank
The best way to prevent the overflow is get a rouigh idea of how much fuel you need. eg: if your gauge reads 1/2 full, then you know you need about 30 to full. So when filling, once you hit the 25 litre mark on the bowser, slow it right down, and listen for the girgling sound, this is when it is almost full.
I cant see why swapping from super to unleaded would make a difference.... I know the nozzles are different diameters... but I have, and all other XA/XB owners I know, have always had problems, even befotre unleaded fuel was available.