It could also be worn bushes in the sliding front suspension.
My '76 sufered with this , on and off, for a few years. Eventually, after a couple of suspension rebuilds it was found to be cracks in the chassis, plus there was growing rust between the chassis legs and the gusset plates welded to the chassis just near the front of the firewall.
"St Morgan's Dance" can stem from a variety of faults - fitting brake reaction bars, as Dave W rightly says, will NOT cure it!
Cheers,
