It will be hard to retain your factory ride and lower the car at the same time. I believe ford B springs are close to the factory specs, probably the easiest thing to do is search on a few mustang aftermarket supplier sites (our sponsors have alot) and see which kit will suit you better.
The C springs are noticeably rougher than factory springs, but personally, I love the ride of them.
"I'm not driving too fast...just flying too low"
-03 SB Cobra vert- 2552 of 5082 Born 02/25/03
90 7up vert - new project-07 DSG Focus -DD