Composite leaf springs om 69 Camaro

[T-T]

Hello there.
A couple of years where I just have followed the various posts, this is my first post on this forum.
I hope that it will give me a lot of response to my humble questions, as I will do anything to help out where I can make a difference.
I've separated my 69 Camaro and seek knowledge and new parts to make it a scary street machine, -ready to give all the "exotic" buy-cars like Ferrari and Porsche opportunities to look at my rear taillights and smoking rear tires

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I plan to buy myself a set of composite leaf springs from VBP to my 69 Camaro.
- Those of you who have the fiberglass leaf springs already installed and running for a while, maybe you can tell me what it gives and takes. -Good and bad.
- In my Camaro, i´m planing approx 500 hp,5 speed manual and I will use the car for street and “semi-serious” weekend autocross.
- Is it possible to order the composite leaf springs 2 inch lowering rear of the car. -or do I have to do it with lowering Blocks.? .. don´t like!
- I've seen people talk about 150 to 210 pounds of pressure/strength ??? ... what can be recommended - please tell from your experiences.
-Can they break ...!!! .. -- is after all just two rods of fiberglass ... or is it??

Leaf spring link: http://www.vbandp.com/Camaro/1st-Gen-1967-69.html

Thanks for all help before I order ....??
Tom –Denmark-