Ian,
I presume you definitely have play in the king pins / bushes?
My '76 had none (after rebuild) but after a short while the shakes returned. Turned out to be cracks in chassis, plus the triangulation plate(s) on the chassis legs just ahead of the bulkhead were being pushed out by rust in between them and the chassis legs.
Tim Ayres / Darren Bunn / New Elms sorted it all out, fitting the plates from later chassis (they are longer) plus repairs to chassis. I also had negative camber plates fitted - better for damping out the vibes (and can also give quicker turn-in).
I presume you have checked for play in the damper blades/shims as this can also lead to shimmy.
