Okay, stripped down frame A and took it to the bike shop to be spread to fit a 130mm rear hub.
Is the saddle to bar drop shown too large? It looks pretty aero in the drops, and he can ride up on the tops if needed.
If he can handle it comfortably, fine. You may find, though, that when he is stretched out a bit more it would be natural for the bars to come up a bit. He'd still be riding with a flat back.