Lessee, in no particular order:
56"s can leave the rear axle stock, which may be best on a K5. I found that my axle pumpkin wanted to become one with the gas tank when I had the springs flipped the other way around. Mind you, that's a 14BFF with a Jethro-Bilt cover, which is freakin' huge. You will need a shackle flip of some kind, which will add height (2-4" depending on type.) If you use stock 56"s and a 4" lift it should match the front (see below.)
52"s will want to move the front axle forward, which is why you gotta do crossover at the same time. (I have about half the stuff you'll need for crossover on a D44/10B if you're interested

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Stock rear 52"s are about the same height as 4" lift springs, so depending on hangers (I went mad) you get about 4" of lift.
Overloads are a try it and see proposition, IMHO. I ended up using six leaves out of my old nine leaf 56"s, and up front I used an extra leaf from a spare set I had to make a six leaf 52". I am not at the moment using overloads, and the height worked out balanced front-to-rear.
I will likely switch my shackle flips arond (again! aargh!) at which point the butt may sag a bit. In that case I may put the overloads back in only in the rear. I am debating cutting them down, either very short as zero-rates, or shorter so they get caught on less stuff.
What else do you need? Well, strongly consider crossover. You might be able to wiggle a longer draglink in there, but it would suck with all that flex; when stuffed you'd not be able to turn for crap.
You will need something to remove rivets. A good torch would be ideal, or a LOT of patience

You will also need a bucket of 7/16" grade 8 bolts and associated hardware to replace them all with.
The 52" writeup discusses the details fairly well.
Expect to remove the springs a few times as you adjust height and such. I've got it down to a science and can swap springs soooo fast now
Anything else, feel free to PM me as I've just gone through this, or of course post up.
-- A