I've not done one of these tanks, but I did modify a tamiya Leopard 1A4 and it had a one piece barrel which had no recoil at all. I cut the barrel inside the turret and made an extension on it so I could tie it into a recoil unit. I have done this on several builds with success. All you need to do is add a piece of brass or plastic tubing to extend the barrel and keep its correct length while still using a recoil system. Hope this helps.