One thing you can always do is just zero out the movement gizmos on both models in 3DsMax so that way their origins match up before combining them into one mesh.
The other option is bringing them into UDK with zero'd out origins and a larger movement grid and snap-to on. It might be a pain to get exactly right after that, but they should be together that way and you won't have to worry about level streaming.
Either way, I wish you all the luck!
