I would say, for right now, don't have Matthew try to interact with Griffin at all. When Matthew comes over, he should ignore Griffin - no treats, no pets, no plays, etc and certainly no putting G in the crate or garage. M should not even look at G. If G wants to go to another room, what's the harm? Hopefully this will help neutralize things. Have you done any reading on dealing with the hard case rescues? There was that article about Queen in some basenji-related magazine recently. If you can find that, read it. (Someone want to help me out about where it was?)
In the mean time, read Control Unleashed, watch the dvd, or better yet, both. YOU work with G on mat work and find some Ttellington Touch exercises. Then progress to the Look At That game, or in this case, do Look At Matthew game. Decrease the distance between M & G, always keeping G subthreashhold. Go at G's pace. Don't push. It is a slow process, but it is worth doing.
If you can find a CU class nearby, go. It'll help you understand some concepts and getting a trainer's persepective will be so valuable.