how much drop?

[SnS C10]

hey guys wondering if u can help me out. i have a stock height 72 gmc 3/4ton longbed thats 2wd. i will be lowering and putting rims on it. im not sure how low i can go though. i will be running a 18x9.5 rim. they will be wrapped with 255/45r18 tires. these tires are 27 inches tall. i want a 4 inch drop in front and a 5 in rear. the rims have a 22mm offset and 6 inch backspace. front will have 3 inch drop spindles and 1 inch springs with lowered shocks and thats it. in the back all i am going to do is replace the leaf springs with 4 inch drop springs and get 1 inch drop shackles. do you guys think this setup will work? will i have major issues with tire/fender clearance? what about the 5 inch drop in back and the axle hitting the frame? if it cant go that low, what do you guys think the lowest i can go is? i have been asking a lot of questions but i just want to be sure of what im doing, thanks a lot for looking- shaun