There are two different styles of valve springs for blowbacks, short-n-skinny and long-n-fat. Sounds like you got a spring kit with not very good valve spring options (which is common). If you don't mind spending extra for tuning, Irish Brigade sells a decent kit on eBay for like $6 that's got 3 mains and 3 of each type of valve spring. There are a couple other kits out there that have extra skinny valve springs as well.
If you're not regulating to low(er) pressure, like below 600psi or so, your stock valve spring should be fine. Monkeying with the springs is most effective when you have all high-volume and low-pressure internals. For me, the difference between springing for 800 psi and 700 psi isn't worth the hassle.