I have a Hobby Engine Abrams and it can be done easily. The barrel is joined down the top and bottom by a seam which once you take the tip of the barrel off, pryes apart quite easily but go slow. Then you remove all the internal cross members and glue back together with an aluminium tube down the middle. For the recoil you can keep the existing housing, just replace the gears and motor with a mini servo modified to work in one direction and connected to a continuous power source. You need to install a microswitch to cut the power apart from when you trigger it.