You don't need the part number mate, all bearings come with a generic bearing number and rather than getting them as Ducati part, you'll be able to get them from any bearing factor for about a quarter the price if you know this generic code. I don't know what the code is for a 98 748 but it may be the same 3 spoke Brembo wheel and spindle size as they use on my ST. In which case I'll go out into my shed and look up the bearing code for ya...back in a mo
The ST front wheel bearing part number for a 2001 bike is 75162.2566. This is exactly the same part number as a 2001 748. Don't know if the 98 bike is different.
The generic bearing code is 6005 2RSR C3. The dimensions of this are approx 45mm OD, 25mm ID and 10 mm width.