I was looking at an english sports car and it had leaf springs and a panhard bar!would this be worth the effort to keep the rear end centered between the frame or is it overkill?

It's overkill.
It is very hard to arrange the panhard bar to have a roll center that is the same as the roll center of the leaf springs.
If they are not compatable, there will be a binding of the suspension under roll conditions.
Some of the old english sports cars use quarter eliptic springs that do not hold the rear end on center very well and require a panhard bar.
The Camaro uses half eliptic leaf springs, full eliptic springs would be like a Camaro spring with another leaf assembly on top of it. The old horse drawn buggies used them.
David

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Check my web page for First Gen Camaro suspension info:
David's Motorsports page (http://ourworld.compuserve.com/homepages/David_Pozzi/)
First Gen Suspension Page (http://ourworld.compuserve.com/homepages/David_Pozzi/first_gen_suspension.htm)
67 RS 327
69 Camaro Vintage Racer
65 Lola T-70 Chev 350 Can-Am Vintage Racer

Thanks David