I uploaded my design for gun recoil for 1/16 Elefant. Works well. The lateral movement could be better, there is slight rotation due to position of lateral servo barrel mount. I have a cast resin ball. It would be better to use OEM type mount. Elevation is by force against castle roof. Barrel needs to have some weight or else you need to add a spring type force against elevation, inside the castle. This is made for tamiya style barrels, but you will have to add a rear barrel extension and a few brass tubes for everything to fit/slide well. The tamiya barrel has a brass tube and rear extension epoxied to it, and this whole unit slides inside another brass tube. Outside brass tube is epoxied to the recoil housing. The recoil set-up could be used in other tanks as well. Servos are mounted low so that there is roof clearance. See the youtube vid and other vids on my youtube channel for more details.
This mount is designed for the spektrum s500 size servos. You will have to sand/file/angle the edges of the servo mounts in order to 'pop' the servo in sideways, after feeding the wire into the mount. Servos are mounted so that they maintain even weight off midline of barrel, and hang down so barrel does not rotate. If you use an OEM type mount, then you do not have to worry about barrel rotation and then the recoil part of set-up could go in sideways...
Note: the barrel is not tightly bound to the 'gun recoil guide.' A single 3mm screw (the black one) is threaded through the gun recoil guide, and passes into the barrel side through a 3.5mm hole. Also, you will have to gently sand down the 3 sides of the gun recoil guid and corresponding surfaces of the gun recoil mount to get a good fit. A minimum of wiggle room needed for smooth barrel action.