It ONLY does it after startup
Generaly that would indicate that oil is getting into the combustion chambers from somewhere whilst it is not running. Usually by seeping down the valve stems.
Could it be getting in through the turbo? a quick plume of smoke being generated as the motor fires it's first charge.
Would get a compression check done if not had one already since the new head.
Irregular maintainace, lack of oil changes, partially siezed pistons etc will all take their toll. So will 'hammering' the motor when cold. Whats the previous history from past owners?
We'd all like smoke free motors . . . . but hey !!! . . . these are Land Rovers :lol: