I used an old pair of roller skates from the thrift store. The trucks were riveted on: I filed the rivet heads off, then pulled the trucks off the boots. I then drilled holes in the combat boots using the trucks as a template. I bolted them together using stainless philip head bolts, washers and nylox nuts. Lastly I put insoles in the boots to protect my feet from the bolt screw heads.
These are not my first pair: I’ve skated quite a lot with used combat boots, and they work quite well.