Another poster asked about a boys' name to match her son Spencer a few days ago. You can see the replies here: www.mumsnet.com/Talk/baby_names/1409984-Brother-for-Spencer. I mentioned some of the names below there but I've tried to amend the list a bit to suit your very sensible tests!
You might like another surname name - e.g. Alden, Blake, Carter, Cole, Digby, Fraser, Griffin, Huxley, Lincoln, Logan, Nolan, Nicholson, Parker, Porter, Rafferty, Reed/Reid, Truman, Vaughan, Willoughby, Wyatt, etc. Maybe there's a gem in your family history you could use. Worth looking into?
Equally, one of these might fit the bill - Alastair, Albert, Anthony, Arthur, August, Barnaby, Bruce, Conrad, Crispin, Dashiell, Dexter, Dominic, Edwin, Emmett, Everett, Fergus, Francis, Gideon, Graeme/Graham, Gregory, Guy, Hector, Henry, Holden, Hugo, Isaac, Ivo, Jasper, John, Jeremy, Julian, Jonah, Laurence/Lawrence, Miles, Milo, Orson, Otis, Pascal, Patrick, Peter, Roland, Roman, Rowan, Rupert, Timothy, Tristan, Wilfred, Winston, Wesley.
I really like Spencer & Lawrence for you - they have a nice ring together. Spencer & Tristan or Spencer & Rafferty sounds nice to me too.