"Plains" era Sioux were past the stoneage. They were actively trading for metal well before they were pushed out of the woodlands to the east and out onto the western prairie. In the prairie buffalo era it is nearly impossible to find Siouxan stone points because common availability iron and steel (and even brass for that matter).
James Hanson, curator at the Museum of the Fur Trade has done an extensive cataloging of axe heads collected on the upper plains. He has noticed on EVERY axe head there are chisel marks on the sides. Along with the records of chisels, hammers, and files being common trade goods this is a fair indication that the axe heads were used as portable anvils for reductive ironworking. Larger pieces such as barrel hoops were reduced to smaller pieces not only for arrowheads but for decorations. Numerous collections include iron hair pieces, conchos, cones, and other shiney bits.
This in no way reduces the accomplishment of turning out such a well made war club just because they used steel instead of stone. You have the advantage of modern steel, chainsaws, and other tools and still find yourself working up a serious sweat to create a copy! Please keep posting photos of your progress, I want to see it finished! I always enjoy your work, medicinewheel. Could you post dimensions of the original as well?
If you can ever get over here to the States, save the cost of a hotel and stay with me. The Black Hills is right in the center of everything! Plus you can use my shop and my tools while you're here.