Considering a rear leaf spring replacement, new KYB Gas-a-just shocks and adding a rear sway bar.

Current springs are 4 leaf. Classic Industries has 4-leaf and 5 leaf and in the description, it states that 4 leaf were used on high performance application but I have read elsewhere that 5 leaf were more heavy-duty (Tamerz). Classic charges $50 more for the 4 leaf ($200 vs. $150).
I am looking for stiffer spring rate and perhaps less bottoming-out when backing out at the end of the driveway or pulling into an incline.

Here's what I've been told. The 4 leaf springs give you the stock ride height from the beginning, but then when they settle (a few years / 1000's miles) they tend to make the rear end too low. The 5 leafs, sit a bit higher initially, but when they settle they sit about stock height. Validity? I don't know, but I believe I put 5 leafs on mine, and it looks stock. I can check this weekend when I get the car back from the shop. I buy my springs from ESPO in PA. They have been great, and always ensure a proper spring. You can find them on the web.

4 leaf will give a good ride & proper stance, 5 leaf will have a stiffer ride. I went with 4 leaf on my '68 a few years back & I like them.

Steve

I like the 5 leafs on my '69 vert.

I have the 4 leaf, now about 2 yrs old , maybe 4-5ooo miles, havent sagged ,but is not that great with people in the rear (which is rare for me , but...)

I have the 4 leaf springs new last year, and I like them. I debated the same issue, and ultimately I was glad I chose the 4 leaf route. I think you will not like the stiff ride from the 5 leaf version. The four leaf has the correct ride height, and I feel it is very tight on the road. New shocks also helped this.

You might prefer the 5 leafs if you are running ladder bars and 12" Mickey Thompson drag tires.

I went with new 4-leafs a few months ago, and I'm STILL paying a fat lady to sleep in the backseat everynight, in an effort to get the rear to come down!!

Thus far its not working, and she is always emptying out the garage frig!! :p