There are a number of things to consider here. First of all, those MP63’s take a taper tip shaft (.355) which will affect your selection of graphite shafts. Second, the KBS Tours are about 120 grams, depending on the flex, and any graphite shaft will be much lighter. Which leads us to the third issue. Some make their graphite shafted irons one half inch longer than their steel counterparts, e.g., 38” 5 iron instead of 37.5” because the overall club weight will still be much lighter. This is what I’d recommend.
The plug in the steel shaft is either lead or brass and was installed to give the clubs a certain swingweight. Depending on what swingweight you want in your clubs, you may need to add tip weights. As you may already know, graphite shafts require special tip weights so they’ll fit inside the shaft tip. Here are 2 links for the 2 different types: https://www.golfworks.com/rubber-tungsten-tip-weights/p/gw0121/
Hope this helps! Michael