The center to center distances are the same, you just need to replace 
     the support bush with a 12v one and grind a little Aluminum off, its 
     because the flywheel is slightly bigger on the 12v.
     
     The fuel gauge, well i've seen folks pay 40 quid for a 12v only fuel 
     gauge. I've been running a 6v gauge on 12v for over a year and it 
     reads just fine. Of course it doesn't read the same as if it were 
     running on 6v, but it registers that you have gas and that's all you 
     need to know really. You could always run it on 6v with a 12-6v 
     convertor. I did an experiment a few months ago to finally prove to 
     myself that the gauge must be reading double though. I conected the 
     gauge to a 1K resitor and a variable voltage source. This is what I 
     read:
     
     V     Ohm     Reading
     
     12v   1K      1/2 tank
     6v    1k      1/4 tank
     
     So it's pretty conclusive that the gauge reads differently, well i 
     didn't really need to do the experiment to know that though coz, V=I*R
     
     
     Lee.
     
     '64 samba
     '60 single cab