The plan is to get the swing mechanism as close to the real machine as I can. So I'm going to machine a custom swing ring and cut internal gear teeth in to it just like the deal.
Here is a diagram of what I have been able design based on what information I have.
The ring will be mounted to a base by bolt holes tapped in the ring, the base will have the bearings for a central shaft that will be mounted to the crane frame. The frame will have rollers that go inside the race in the ring, like this.
Shawn