Rear springs convert for lift?
 

Hey all
I have air suspension and I was looking to do the Egan mini lift.... of course this consists of springs in the rear. I heard you can convert air to springs, but i only heard you can do that with stock parts.
1) is this correct?
2) if so where can i get these parts used?
3) if it can be done without the conversion, what kit do I need to get to convert?
4) is there a way to convert to springs but still keep the airbags in case I tow or something