FS 650 vs FX 650 '2005 engines

Hi everybody.
My English isn't very well so i couldn' found any information here. And there is no information at Russian forums.
I want to buy husaberg. it is 650 2005 year. But I have a problem. The bike was rebuilt from FX 650 into supermoto. And seller doesn't know what engine has the bike. Is there any difference in engines (excluding )?
it is very important for me because i want to use it for everyday city-riding. And if it has FX engine and it needs service depending on hours (not on the distance) i can't use it as everyday bike.
I try to find any info - but i couldn't. Also that bike is with electric starter, but seller says that it wasn't in stock.
Thanks!

Thanks. The bike is in another country and it is near 900 km to go there. Don't want to make wasted trip. Husaberg is very rare bike in my country to get advice fron anybody.
Aha, the year is 2003, and engine number is 5013145.
So there is no 650 but 501 engine, 145 - serial number. and what does it mean? ))