Advice on lowering a 70 C-10

[hotrod363765]

Hello and Merry Christmas to All you old truck guys.

My son and I would like to lower and airbag his 1970 C-10 longbox. So if we run 18's on the front and 20's on the rear how low can we go? I figured on C-notching the rear frame and dropped spindles on the front. How far can you go without getting into the front wheelwells? I also want to switch to a 5 lug pattern, easy on the front.... disc brake kit, but on the rear I will have to pull axle shafts and redrill a new pattern to get a 5 on 4.75 or is there a easier/better solution? Can anyone help me out with tire sizes and backspacing suggestions? I have good fabricating skills, lathe, bridgeport, tig welder...so I can do the mods. Any mods to the lower control arms? what kind of mods for the rear arms? I see the Porterbuilt front and rear kits, they look nice, are you guys good with their stuff? I'm sure I'm overlooking some things, so school me on what needs to be done here, this is our first truck! thanks, Jeff.