I decided to match the driver's hatch openable, so that means I need a driver. In order to get his height right (and make my intended hatch fit, it meant that I had to seat him a bit lower. So I carved a hatch like the one on the left into a much smaller seating ring (center), to which my driver could fit.
The next problem to overcome was that I needed to make the turret sit a little higher, so that when it traversed, it wouldn't bang into the driver's hatch (which was ending up being a bit higher than I originally planned. So I took one of the hatches left over from making the front grilles (left) and trimmed it down to just leave the ring itself (right), which then I had to shave down a bit so it didn't look too high.
The next step was to fill in the various gaps I had created with green stuff (well, in this case, brown stuff. I also needed it to fill out my driver's hatch, which I wanted to be more complex than just a circular hatch.
Next I laid out the turret pieces. I wanted to use a Predator's turret, but the autocannon was a bit too long for what I wanted, so I lopped it off and replaced it was an autocannon from a Imperial Guard Heavy Weapons team. The "grittier" look of the IG autocannon makes it look more IG anyway compared to the more high tech look of the Space Marine autocannon. I used an old Leman Russ hatch, the SM "scanner" thing from the Command Vehicle sprue, along with some other antennae you don't see here, and put in a coaxial heavy stubber. This is a command vehicle after all, so the turret is going to look pretty busy. Also, for the left side of the turret, I glued together a pair of ancient Leman Russ Hunter-Killer Missile containers.
To attach the Hunter-Killer Missiles, I wanted to be able to have the containers down and locked for when the vehicle is travelling, and then swivel up into a firing position when needed. This necessitated some surgery--so I used a couple of pieces from the ancient Leman Russ sprues and paper clips to make the hingle-bolt. The parts I used are mounts for the old Leman Russ' Hunter-Killer Missile container and searchlight.
Here is the assembled turret--I put on some smoke launchers and a second antenna. The second antenna is the IG antenna from the command vehicle sprue--frankly, I hate the Aquila shaped antenna, so I replaced it with a small dish from the SM vehicle accessory sprue. I just pinned it in place so it can rotate.
Here is the turret with the Hunter-killer missile rack in locked and deployed configuration.
By now it should be pretty obvious what the inspiration for my command vehicle is. Here, the driver's hatch is just sitting there--I don't have it attached yet, as I'm still trying to figure out how I want to do it. I still have lots of bitz to add, but I'm getting closer to completion.