Lowering my 55 Fairlane but I'm confused

[Dorf55]

I have a 1955 Ford Fairlane and I'm looking at lowering about 2" in the front.
I will be using blocks in the back, for the front I'm thinking about placing a 1" square tubing as a spacer on the spring pocket and extending the spring pocket.
This is when I become confused, I have seen a few articles on this and they all give different final lowering numbers, I have seen 1 1/2" up to 2 3/4" drop.
I would think if I used a 1" spacer I would get a 1" drop and so on, please let me know what I'm missing I would only like to do this one time and get it right the first time.
Not sure if it makes a difference but I'm running Aerostar springs.

Dorf55