What is the gapping distance between the valve spring and rocker arm?

Check your shop manual, but that said if my memory serves me well if it's a 3.0 v6 engine. Once its back together there shouldn't be any play Theres no adjustment once reassembled, they should be good to go. The hydraulic lifters will take up any slack once they fill up with oil and build pressure after the engine runs a bit. I hope this helps good luck.

Thank you so much for the answer. Do I retorque the rocker arm after changing the lifter?

Yes always re-torque all bolts back to factory specification upon reassembly.