DJM 4in control arms question
 

I have these control arms second hand and never used at a great price. I have the insructions and it tells me to install with 2in lowering spring. I wanted to drop my truck 4in up front and 6in in the rear (flip kit w/c-notch). Has anyone have info or knowelege to why i couldn't just use my oe springs or is it an alignment issue, ride quality. 1997 silverado extended short bed.