I'd try to photograph from the front, the subjects with crossed arms, slightly leaning against the other one's shoulder.
That means you don't want anything experimental or too far out there. There shouldn't be a noticeable pose. It should not look too staged.
I don't want to do the two men shaking hands shot/pose.
That's a great pose if there's anything to shake hands for, but if there's not, it's out of line.
There's another problem with the shaking hands pose: From experience, we'd say that if we see them shaking hands in a photograph, this is such a rare event that it was worth photographing. This is not the story you want to tell. You don't want to take that "ok, we won't destroy the planet"-type of cold war era hand shaking portrait upon singing some let's-not-destroy-the-whole-planet treaty.
portrait shoot that has a personal angle to it.
Also, the two subjects usually look at each other, which shows some kind of confrontation. You cannot portrait a friendship if both subjects looked into a different (opposite) direction.
If both were looking into the same direction, but you photographed them more or less in profile, you'd get a very iconic look. That can suggest strength, but more importantly, it suggests some distance to the viewer of the image. Both subjects looking to the left (or right) of the image suggests that they have the same opinion (there's connectedness between them), but they don't necessarily give a damn about you (the viewer)
This is why I think that both should look into the camera which is in front of them. It's an honest look at the subjects. "Hey there, this is who we are".
Having them lean against each other is the way to tell friendship in a professional sense, because the part of what makes a friendship that's important in the professional world is reliability: "I could lean against a solid wall, but this guy next to me is just as good", but you don't want to overdo it. It should not look like they need the other guy to stand upright. It should look like they do this because they can do it and not because they have to.
Last but not least, the crossed arms. This is more or less for lack of other way to place them. It works well with the leaning shoulder-against-shoulder pose. If the hands were free, you'd have to come up with some pose for them that's not too meaningful. If the hands don't look boring (by hanging down), they are suggesting something. Getting the hands in a pose that suggests the right thing (or at least not a wrong thing) can be tricky and hard. Crossing the arms eliminates the problem of dealing with the pose of the hands.
If this is full body portrait, I'd suggest that the legs should be straight. Both feet on the ground. You want to express stability.