You should watch the videos that Erik made about the airsoft recoil turret for the Tiger One (if you haven't already). They really give a good basic understanding of what you need to do to make a barrel recoil work for airsoft. I've been playing with them a bit and one thing I want to try is a full length inner sleeve for the barrel. The way the Tiger One barrel is set up there's a gap between the end of the barrel that fits the airsoft unit and the barrel that's attached to the muzzle brake. I'd rather have a one piece barrel.

Another thing you may want to think about is adapting the Imex servo board. You said you want to keep the track recoil (that's usually the first thing guys want to disable), so you may be OK with stock electronics. That may be a better fit for your budget, as well. Is the new King Tiger 2.4 GHz or the old style RX-18? That might not make sense to you if this is a first tank, but it helps identify when the tank was produced. Can you post a link to the tank you bought?

Do you need a link to Erik's youtube channel?