which springs to use?

I have a similar setup. I have weld in subframes and Eibach drag launch springs. The subframes will just make the frame stiffer, launch straighter, etc. Your spring delema really just depends on what you want to do with the car. Most guys go one of two ways with thier cars. They either go for the drag racing type mods, or the road racing mods. Some mods work well for both, but some are specific for thier intended purpose. Some common drag-only mods would be: no front sway bar, drag springs, skinny front tires, drag shocks, etc. Some common road race mods would be: very stiff lowering springs, larger wider wheels on all four corners, strut tower braces, heavy duty sway bars, and any kind of chassis stiffening device possible, etc.
It sounds like your car was previously being built in a drag style. Drag springs aren't going to be "dangerous" on the street or anything, but they are not made for heavy cornering. They are designed to squat in the rear and pop up in the front upon launch. In my case, the Eibach drag launch kit lowered the rear some and raised the front alot. My car leans back a good bit, but this is supposed to be good for weight transfer when drag racing. The look is not for everyone, but it has a purpose.
So it really depends on what you do with your car and how you drive it. I've gone the drag-race route because I like right-off-the-line performance. I'm not much into corner-carving, so it's not a problem. If you wanted to get a differnet kind of spring set, you could always sell the drag-launch kit. There are plenty of people who would be interested in them, I'm sure.
Hope this helps.

Here's a pic of my car with the Eibachs...