andy_sr, OK, I need to make a few assumptions here, but I think I can lead you in the right direction. First of all, I am assuming you have the screw-in weights that came with the Kinetics. These were 4 gram weights in the toe and heel. We make and sell 2 gram weights, so that would help some in the head weight department. I would simply go 1” over standard because no one I ever knew could come up with 1/4” increments. So, we are talking a 39” #5 iron. 1” over standard is 6 swingweights increase and we can remove 2 of them with the lighter weight screws so we are going to get 4 swingweights heavier with the XL Lite shafts which I assume are an “S” flex. I am recommending that you go with a True Temper Dynamic Gold shaft in parallel tip and S-300 flex. Your son at 280 yards with a driver is at the high end of “S” flex and the low end of “X” flex (have you ever had his swing speed checked with a driver?
The Dynamic Gold S-300 shaft is about 10 to 15 grams heavier than the XL shaft, so we will reduce the swingweight by about 2 points more (heavier shafts require lighter head weights to maintain the same swingweight vs. lighter shafts which require heavier head weights to maintain the same swingweight, so trust me, the swingweight will be reduced). Assuming you were a D-2 at 38” on the #5 iron we are now at a theoretical D-4 at 39” which is no problem. I went with the Dynamic recommendation because it is tip stiff and low torque which is what we want when we go this much over length. He will have plenty of feel at this length and he will have better directional control.
Check the lie angle using the lie board or something to determine the correct lie for him. Keep this in mind, for every ½” you lengthen a club the lie angle appears 1 more degree upright. So the 1” length change will automatically make the clubs appear 2 degrees more upright to the player.
I don’t think you will need a butt extension except if you are making up a 3 iron in the set (I am assuming starting with a #4 iron here). Also, when you get to the #9 iron, make the PW, GW, SW and Lob ¼” shorter each. If no gap wedge is used then go ¼” from the PW to the SW and a ¼” to the lob. I know I like to keep my wedges at ½” increments and I often recommend this but it has always worked out better with very tall players to go ¼” mostly to save their backs.
Also, go 1” over on the hybrids and the KE4 80 shafts in “S” flex will be OK. Now, I know we are not talking about drivers, but I sure hope he is not playing a driver over 45” long. There is no need to go 1” over on the driver. Even tall tour players stay at 45” and they sometimes have longer iron and fairway club lengths. You simply loose too much directional control for the small increase in driving distance. Remember to get the small increase in driving distance you must hit the ball on the middle of the face. This becomes increasingly harder as the driver club length gets longer. It’s amazing the number of players who actually hit the ball longer with a shorter length driver because they can hit on the middle of the face.