With a system like the TK40 you use a 4 channel radio, so once you're radio is properly set up your right stick will handle motion, forward and reverse and left and right turn, and you're left stick will handle turret Rotation, gun elevation, as well as firing the main gun and the machine gun. Elevation and Gun fire are all on the left stick, up and down. Push forward a bit and you get elevation, all the way up for main Gun, down for MG (at least on an IBU, Clark also uses half stick controls). If space is that tight, you might use a modified taigen v3. I did this in my Tauchpanzer and it's been fine, I removed the entire case and just mounted the motherboard itself. You lose the fan like that but I talked to Erik at Imex and he was confident that for normal use it would be no problem and the fan is really a precaution for extremely heavy use. That made it small enough to mount on it's side next to the battery box, a very small space. So far the Tauchpanzer has been fine and drives like a dream. No sign of overheating at all. I'm just using the stock TX but it's set up to use a hobby grade 6ch radio if you want.

You want to do 2 tanks, right? This is a project that interests me so maybe I can help. As soon as you have 10 posts, post some photos so we can tell what you have. If you have trouble with the photos you can use a host like imgur and if you're not familiar with that we can easily walk you through it. Have you opened one up yet? Photos of the inside will be important.