3/5 Lowering Kit.....Good?

[78' Silverado]

Well...I found a Lowering kit for my 78 Silverado Short Bed. Its from Western Chassis, I am getting 3 inch Lowering Springs in teh front and a 5 inch flip kit in the rear. Right now i got stock front end. And 8 leaf springs in the rear with 2 inch lift blocks lol. Yea its a stink bug :P Anyways.....after the block come off...yall think a 3/5 is a good drop? MY main ? is....Are they hard to install?...I mean can it be done in a weekend? I really dont kno much about Lowering at all. So I really want yalls feed back on this. Also....Another reason I cant go to low is my tire size. My tires size is *P235/75R15 105S* I think a 3/5 will be kool. But If i can I wanna do a 4/6. But I cant find any kits for it lol. So....yea I got alot of ?'s lol. Oh and also...Will I need t get new shocks?
Thx alot guys!!!!

Tyler