RE3.5 + bastad pack

okay, after a lot of reading i am considering going with the parts from a RE3.5 lift and bastard pack. Since Re lifts seem to net a little higher then adverstised, and i dont have a new bumber or winch, should i build a bastard pack for 4in, i am not really sure how high to go since i want to keep it as level as possible. I have a 3in leaf on the rear right now, should i just go a head and add new shackles instead of the bastard pack or will that put the rear up too high. last thing, would i be able to re-use any leafs from the 3in pack or would it be better to go with the XJ main and s-10 leafs. i am thinking about using the main, plus the 2nd,3rd and overload. will that even the rear out with the front or would guess and check be the best way?