It looks like a Petter PH1 water cooled. Or also a AV1.
It could be either, and the easiest way to tell from pictures only is the injector, but as the fuel injector and pump are not original, there is no way to be certain from pictures alone.
So I found some additional info and it looks like it's defiantly a petter AV1, is this a model that is copied by the Indians and has a decent parts availability?
If it is, it will not be 10HP as per the auction description, plenty of spares available from India, from all the usual suppliers.
Looks to have many non original additions.