I made a front spring out of a old bed spring and election sign wire. It came out pretty damn good. I would put it up against any original spring. The only difference is mine has smaller coils and that makes it a little firmer. People weigh more now. You would need a welder to make what I made. If you're considering trying one too. I noticed that every original spring I saw was rusty, some very much rusty and some not so much, but all were rusty. So I painted the ones I made with a "rust Paint" like Ben Moore's "Rust scat" This does the trick very nicely. Try to stack two or more springs and spray downward. Shift them a few times to get coverage and I think they will be fine.
Terry