I think the nv4500/atlas is such an awesome combo - but just a little too pricey for me. The catch with the nv4500 is that it's a dodge hence the need to find conversion parts to mate chevy/ford parts to it. Advance adapters sells it all no doubt and decent parts. I've run a few of their obscure parts, i.e. a ford np435/205 up to a chevy 350... without any trouble and some major beatdown.
I'd say it really depends on what axles he gets. Have him find the best deals on ford/chev axles that he can and that'll determine the rest of the drivetrain. The np205 is something to swear by in terms of durability and ease of acquisition, but there are no gearing options for them and a rover might not have a long enough wheelbase to support a doubler - not to mention the fact that all doubler setups with the 205 weight a LOT. The 20 sounds like a great option, small, lighter, bomber and has lower gearing options. Although none of which are cheap. That and adapters to the 4500 are not cheap either. It depends on the budget. The cheapest in my mind without considering lower tcase gears is just going with the dodge 205 and match with good axles... cheap, simple, easy to find drivetrain equip. How much cash is he willing to toss down is the simple question.