Not to hijack the thread but this is the same thing I was considering doing. Going big block and what to clear 37" tires with good articualtion. Will 56" springs on all corners get me there. I am sure I will need zero rates and/or a small body lift and trimming.
With lots of flex you're going to need to trim the front fenders quite a bit, doesn't matter if you stick with the 4" or so that the 56's will give you or if you get it a couple inches higher with zero rates and body lift after that.
Basically, if you want flexy you're going to have to trim.
56's all around and 37's works great IMO, remember that you'll need a shackle flip for the rear.
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