Can I assume that your truck has stock rear springs? I don't know where you are at, but sadly I gave away a full set of shocks yesterday to a local friend. If you are trying to keep cost to a minimum, I would get an extended shackle and blocks to lift the rear end.
If your front is lifted 5 inches, expect them to sag at least 1/2 inch so I would suggest one of the following combinations:
(1) 3 inch blocks and 2 inch extended shackle (3 inch is the max reasonable lift block and Marlin sells 2 inch shackles.)
(2) 2 inch blocks and 2.5 inch extended shackles (less axle wrap, All Pro sells shackles this long.)
What brand of front springs do you have?