I'll go a bit against the grain here. On my old 64 swap I used a 4 + Overload pack from a random truck spring shop here. They had 3 different load options, and I can't remember exactly what it was but I went as soft as I could with 4 leaves. I think I remember 190 lb/in rate, but don't quote me. The overload is like a 600 lb/in.
I let my springs over-arch to get the stuff. Ditched the overload, but had to keep the W in check. So I grabbed some old springs from an S10. I can't remember which I used but I pulled a thin leaf out and cut it down. Its arch is very much so deeper than the 64's. I put that leaf at the bottom of the 64 pack just to help the pack keep its arch shape and not W.
I really didn't expect much life out of them. But they made it 5 years before they should have been replaced. While not near as good as something like an ORD pack, its an option that I don't think you should shy away from just because it goes against the matching rules. I was certain the shape-keeper leaves would crack. They never did.