Obviously this isn't a M900 or 900SS engine as advertised: https://www.ebay.co.uk/itm/17763383...qeKbg==|tkp:Bk9SR-jBu6DbZg&LH_ItemCondition=4 It looks to me like a shallow sump 999 lump ripe for a rebuild at the low price. But what's going on with the engine number that looks like it's bee re-stamped:
It looks like it's been over-stamped with a row of 'B's, including a couple of the webs below. Seems like an odd letter to over-stamp with, and isn't making any attempt really to change the identity of the engine in a covert way. It would be obvious to anyone looking that it's not right. Does this mean anything specific to anyone? Is it code for something specific? Perhaps a particular race team marking their engines?
I'm not so sure it's suspect in a criminal way, as the number has been changed in such a way it's obvious there is something different about it.
I doubt Ducati could help you with the number? If you want it buy it, use it for spare parts? Seems cheap enough.
Walk away. It is either nicked or from an insurance write off not allowed back on the road. That stamping will always cause you problems. We used to call these type of things Boomerangs, as they will always come back (usually to bite you on the arse).