Brief update.
Whoever suggested “check all fasteners” was spot on. Found front prop-shaft bolts loose hence the hollow clunk sound when load taken an or off the drive train in first or second gears, now sorted. In fact found lots of loose bolts, all tight now.
Did find a bent axle u-bolt hence replaced and also put anti-tramp plate the right way around. Previous one was upside down in an attempt (I think) to avoid interference with the floor/angle section at the back of the bulk head, so cut small section of angle iron away and refitted correctly.
Cleaned springs and applied a lot of chain lube, so far seems to have worked well.
Have new radiator from SiFab that will be fitted soon as original rad. is shot.
Stuart