The rear sight is fairly easy and there are alot of fixed sights available. Kings, Novak, Heinie, all make nice units. The front sight will be your main problem. It's staked in place so changing them usually requires a special tool to get the new one on. You can install one without it but you need to be extra careful and in general handy with tools and guns.
You can try to cheat a bit to. Smith & Wesson has a Novak style rear sight made in plastic for the Sigma and MP 22. Nice sight picture and the plastic is easy to work with to fit a 1911 dovetail cutout. For the front you could make one out of ABS, Delrin, or another plastic and epoxy it on. Should work fine for plinking.