A chain that is pruned and contains events like results of consensus. Not the results of a PUT. And that is the difference. A blockchain (== database) is not the same thing.
Yes you can use SAFE to store securely a blockchain by using MDs or chunks. But the datachain is tailored for recording events and that is its purpose.
blockchain == database tailored & specialised for crypto transaction ledger
datachain == database tailored & specialised for consensus & events ledger and is pruned. (ie transactions consolidated and removed)
I doubt trying to manipulate a datachain for use as a blockchain is worth the effort or is even possible. If you could manipulate the datachain for use as a blockchain then its no longer a datachain, even though both are specialised databases. Just like I could manipulate a motorbike to become a snowmobile, its no longer a motorbike even though both are motorised transport.