Lowering and C-notch

[Del72Chevy]

Has any one lowered their 71-72 rear with a 4" coil and not used a c-notch. I know all the books and manufactures recommend a notch when lowering 4 or more but I was wondering if it is just a ploy to get you to buy more. Right now I am measuring 6" between the bottom of my bump stop and top of my axle so if I lower 4" I should have 2" of play. Would that be enough for travel without having the bump stops slam the axle? Also this may be a stupid question but is there a way to tell if your coils are stock or not? I would be really mad if I ordered a 3" coil and installed it only to see the truck drop 1"