Right, sorry for being quite so long on this project, did a lot of work on the G3 last summer and work has been very hectic the last few months, however . . . after much deliberation, trials, experiments I have come up with a solution for the larger parts that I could not make by photo etching.
I had a requirement that the parts had to be extremely light (working model, don't want it to roll over) - No metal castings, they had to be thin walled - Resin castings were tried, but the thin walls gave a lot of problems, I needed a lot of vents and they had to be consistent - hand building techniques could not produce the accuracy and consistency.
So it was time to think out the box!
The solution I felt was right for this model was to use a relatively new technique that I have used before in my work - Stereo lithography. The general concept of this process is the build the components required in 3D CAD and then a very cleaver computer program slices it in to thin layers and rebuilds the model in the real world out of resin. There are various ways of doing this, but the process I found and used after 6 months of investigation builds the model in 0.04mm thick layers so the resolution is very high.
The final computer model looked like this and is drawn at 1/96th.