First of all, bear in mind that I didn't "modify" the BUSA structure but rather trashed it entirely and built a new fuse almost completely from scratch based on the Joseph Nieto technical drawings, which I had blown up to match the BUSA wingspan. I don't think I'd recommend this approach, particularly on a first model.

With this in mind, the rudder and stab/elevator on the EIII were referred to as "full-flying" meaning there was no stabilizer or fin as on the BUSA version. Doing a full-flying rudder would be a fairly straight-forward modification. The full-flying elevator is a bit more elaborate and also makes the model a bit harder to fly. Note that both the rudder and stab/elevator on the BUSA eindecker are considerably larger than scale. I also moved the wing position forward to it's scale location. You'll need to think hard about whether you want to mess with the aerodynamics of the model.

I think this is wise. You seem to have both the skills and desire to do serious scale building (and I welcome you to this teeny fraternity) but you might be better off just playing around with basic mods on the BUSA kit. You've already got a great start on that with your built-up fuse structure.

Thanks, the tail skid support is one of the characteristic features of the EIII so I wanted to replicate that. The basic structure is music wire in styrene tubing.

As I said, I completely scratch-built a new tail, elevator, and rudder and had to come up with my own mounting methods. The rudder is mounted on a modified tail wheel bracket. A music wire runs through the bracket, through a tube in the rudder and into the skid brackets below. The full-flying elevator is built around a central aluminum spar that slips through a styrene tube which was then attached to the rear of the fuse. I was probably naive in doing all this which was also my first RC build.