To just replace a link you need a mallet and punch and a suitable jig to hold the barrel in place and protect the bottom lug while you pound out the link pin. Fitting a barrel is more involved. If it is a "drop in barrel" then installing a standard link and bushing may be all that is required. A "semi-drop in" part will likely take a little fitting around the barrel hood extension and the outside of the bushing as these barrels usually come with the link installed and a bushing matched to the barrel. A full gunsmith installed barrel will require the upper lugs to be dressed to match the slide perfectly, the hood extension will need to be dressed and the lower lugs cut so that they ride on the slide stop pin and keep the upper lugs firmly planted in the slide. Then the bushing will need to be fitted to the barrel and slide. Once that is done, the chamber may need to be finish reamed to get the correct headspace.
