Hi avel,
I have choosen to build the model without iron parts because it's made for the work and by time is unavoidable that paint wear out and i prefer to don't have rust. So the project is born mainly with aluminium, brass and stainless steel.
In this configuration the center of gravity is very close to the axis of the swivel flange because the full metal undercarriage and platform plus the ni-mh batteries already helps to draw back the CoG. On the other hand the aluminium boom and stick are not so heavy. So i have no reason for trying to draw back more the CoG maybe with iron counterweight.
See you, my greets.
Enrico