drop spindle and spring question

[DS3685]

Hi everyone I just picked up my first C10 its 70 swb truck. I am goin to do the disc swap in the front with 2.5 drop spindles and i wanted to buy the lowering handling kit from classic industries and the kits are listed with 3\5 drop fro stock spindle or 1\5 drop with drop spindle. Im asssuming you cant use the stock spindle springs with the lower drop and the drop spindle? Will I have to buy the front springs separate to achieve my goal of lowering it around 5.5 inches? Thanx in advance any help is greatly appreciated