You'll end up with Grated Humpback
The thing about cobbelstones is that they are not a smooth surface. You're dragging what is in essence
150 40 tonnes of whale meat over a large grater.
250m I don't think is long enough to grate the entire whale down, but you're going to lose a lot of it to the road. Also, you're going to have trouble with connecting the whale to your haulers as if you anchor the whale to the ropes via the logical points, the base of the skull, within 100m your crew are either going to be dragging a head (because the rest of the whale ripped off because of the friction with the cobblestones) or you're going to be dragging a head and a spine (because it ripped out with the head, although I think this is less likely).
Whale meat and blubber is not as cohesive as (say) metal. You can cut whale meat with a knife, for instance. And you're dragging 40t of it over a bunch of coarse, sharp stones that act as knives when it comes into contact with the flesh. In point of fact, that's the only reason I'm suggesting it will take around 100m for the head to rip off; the first part of the whale (after the skin) to be ground down by the cobblestones will be the layer of blubber. This fat will act as a grease, greatly improving your haulage of the whale until it runs out of course, and then the meat will grip to the cobbelstones like a rubber tyre and the head will come clean off.
NB: you might be thinking that cars travel on cobblestones all the time, but this situation is more analogous to pulling a large truck along cobblestones with the handbrake on. Don't try doing that at home.
Do your village a favour; invent the wheel and the knife. Cut up your humpback at the shore, put it on carts and haul it into the village like everyone else did throughout history. It's simpler, less waste and requires far less manpower as each cart team can come back to the shore for another installment of whale.
Historically speaking, most whaling boats used to even do the processing closer to the catch, in that they rendered down most of the whale directly on (or more to the point, beside) the boat. Put simply, the primary uses for a dead whale involve using various parts of it, not the entire thing in one go. Incidentally, it's also easier to handle in chunks (no pun intended) than as a whole. As a result, you're actually far better off processing it closer to where the thing is caught (or brought to shore) so if you can't have wagons and knives, the other solution is to bring your processing plant closer to the shore in the first place.
Put simply, 250m of whole whale over cobblestones is a really good reason to build your processing plant by the shore, or cut the thing up beforehand.