You are NOT moving 3" or 4" in the front only the width of the frame rail or a little over 2".
Well that's not actually true Rusty.
The front of the spring eye is moving about 4". The outside point of the spring eye moves about 4".
Although in some cases this is actually a good thing because it moves the instant centre.
You'd have to break out the slide rule to figger it all out.
I'll take a measurement of a stock location spring set and post.
If someone wants to measure the nonstock location and post we can clear this up.