Hello Ed,
I own a 1962 3.8 MK2, and am in the process of restoring her. I plan to stiffen the suspension for road use (not racing).
I intend stiffer front springs, additional rear anti roll bar and possibly additional coil springs for the rear. I shall replace the dampers with something like Koni's which can be adjusted and I shall replace all the bushes with polyurethane and also try for a little negative camber on the front. (An easy adjustment) My aim is to cut down on roll and also reduce the understeer that the standard set up has.
There are kits on sale in the UK to improve the MK 2's handling, but at a price.
If you want to race, then lower, stiffer, and better location for the rear axle. Another popular modification is to fit an XJ6 rack and opinion steering to improve the accuracy of the steering.
Hope this helps.
Iain