How about a Chrome Moly framed TYZ with a sidecar. This is ridden by two of our local riders and have who a number of Australian Championships on this including the current title, so the bike may be past it for solo but it is still setting the pace in sidecars.
As a point of interest the whole frame including sidecar only weighs around 2 kg more than the solo frame it replaced. it has done around 5 or 6 years of sidecar work and I don't believe it has ever cracked. When you see what these guys ride it is amazing.