yes those springs are fantastic, and with the adjustables shocks, you can dial out most of those harsh bumps mid corner.
What the Datsun needs really is negative camber in the rear (about 1-2 degrees) and that is the achillies heal in rear live axles that it will twitch on fast sweepers if they hit a bump dus to lack of contact area of the loaded tyre to the road surface.
My new coupe has such a rear axle assy with 2.2 degrees negative camber built into the axle housing, JTS springs and Spax on-car adjustable shocks made in UK....
havent driven it yet but high speed sweepers will not be a problem.