I did 5.4 Super Duty springs in the front and no rear block in the back. It fit my 305/55/20 Toyo Open Country AT's just fine with 20x9 BMF Novakanes. That tire is pretty much a 33/12.50/20. I could have gone lower in the front and rear with those tires.
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mine is pretty much like Jeff's in this pic same front coils . i pulled the block and the thick rear and overload springs just to see how low it would look . my tires are like 32.5" tall but still i think you could do it .Up front you might be able to cut a little more coil and trim your bump stops .