I had a Marshall 1960B and I tried running it as two separate 2x12's one time and didn't like the result, it's like there is to much extra "air" inside to run it as a 2x12 and it just didn't have as much punch as a regular 2x12. I'm not sure if there is a way you can get an A/B/Y splitter or something so you can switch between the two and use the full cab for each of them, but that's something I would look into. Either that, or run 2 2x12 cabs.
I like the G12H65 and G12M speakers over the G12T75's as well. The G12T's have worked for me when mixed with other speakers (Had G12T75/G12H30 x-pattern that was cool), but by themselves I though they were kind of dark and muted sounding. I've never mixed the H65's and Greenbacks, so I can't say for sure what they'd sound like together, but they are definitely two of my favorite speakers.
That's all I would personally change, it sounds like a very cool rig! I've had some modded Friedman's and those amps are awesome!