Hi Nick,
If you want a lightweight Newtonian then I'd recommend a conical mirror mounted with a single bolt though a backplate. A tiltable piece of ply is all the mirror cell you'd need in that case.
This is what I'm currently building, for a Royce 12.5" mirror:
http://www.rolfolsenastrophotography...4423&k=vcnLTsG
Cheers,
Rolf