Harry is completely correct these springs are no where near a modern well set-up IRS car however over any other solution as far as a 1200 is concerned I know of no better spring. I do know some people Chris (aka Dattoman) on the club has converted the rear to a 4 link setup, however he has yet to prove it in race conditions.
Also if you go for this then the forward upper leaf spring mounting bushes need to remain stock as having nolathane in then ties the back up too much making the high speed twitch worse.
I think what myself and Harry means by mid corner twitch is that the car wants to swap ends especially when you are about to apply power this is not what you want to happen.
The rear camber did dial alot of that out and the yellow car around the same track with the same engine was considerably faster with the same rear setup...only thing different was the camber.
I dont think a sway or pahard will help much its the contact pad of the tyre which is compromised at this stage. You can see here in this photo the rear really fighting for grip in mid corner compared to the front. the sidewall is bending over itself and the contact pad is minimised.
[img]http://datsun1200.com/modules/myalbum/photo.php?lid=5882&full=1[/img]

This would be especially bad in Harrys car cause of the extra power he is carrying and speed into the corner..it would be un-nerving. However again its the best setup that i know for a 1200 at this stage...