Have you talked to Miller about this? If you get to the right person they can be very helpful. From looking at the parts list it appears that there is a different transformer part number for each voltage. On the other hand, it appears there is a 23o volt winding for the fan motor that would give the correct turns ratio for 230 volt input. Obviously the fan motor leads would not have the gauge to power the welder, but if that winding is in fact a segment of the main primary winding, and there is access to it at both ends, you might be able to do something--such as use it for a "center tap" and run two sections of the primary in parallel as one does with a dual voltage motor. Obviously don't mess with something like this unless you know exactly what you are doing at all times (!) One would need the winding data sheets from Miller, or to strip the transformer down, to really know what's what.