I called Eaton and got the stiffest springs they sell for a galaxie but i'm after handling and my car had 6 cylinder springs. If your car had a 390, I would guess it weighs similar to a 460. you have to look at the total front end weight and what kind of ride / performance you are expecting.
I see you are building a 64 galaxie. Well, I bought my wife one for her birthday and I am rebuilding it for her. I also have a 460 w/C6 trans going back into it. Is there anything that I need to be aware of when putting this engine/trans combo in this car?