After many delays (engine rebuild in another car), the culprit turned out to be the rear shock absorbers.
This was somewhat surprising at the noise is evident when driving over the smoothest concrete surfaces.
Rebleeding the shockers made a difference initially but after a few days the rattle came back.
Ny Ute is fitted with old-style spiral bodied shockers and I've been told that they are valued by restorers.
Any one like to make an offer?
Cheers,
Tony