He doesn’t have a design mock-up, he has nothing more than a layout mock-up.
That said, I would suggest that he takes some elements that he likes from the previous website (assuming this is a replacement) and see if they can be re-used.
Visitors, in my experience, aren’t great fans of complete refreshes…they like things to stay (mostly) the same. That’s not to say that a complete overhaul isn’t sometimes beneficial but if you are targeting a specific audience it is only logical to keep doing what they like.
If this is NOT a replacement, then a search around some template sites to see what KIND of things he likes might be beneficial.