I assume you ordered an airsoft King Tiger? I think your best bet may be to study the recoil unit in the Imex Tiger one with airsoft barrel recoil. That will give you the basics of how everything has to work. The clark unit may be a good starting point, but I do believe it's made for IR tanks and the needs are completely different from airsoft. I've actually been working on a universal recoil set up for airsoft but it's still a long ways from finished.

You also need to decide what your final goals are. It sounds like you want an airsoft King Tiger with working barrel recoil, but I've found it's best to be sure so there's no confusion. Are you trying to incorporate any other features, or will you be happy if the barrel recoils and a BB comes out?