Yep that is how it is done. I put one on a KM77RP MKII in .223 for my Son-in-Law. Result, one sweet trigger. In addition to the fitting of the safety already mentioned, there is also a tiny bit of stock material that had to be removed to allow room for the overtravel adjustment on the Timney Trigger. This too was quite easy.
However the exsisting trigger can also be tuned to be super. I have tuned about a hald dozen of the Ruger Triggers, and the exsisting trigger can be made super crisp, and safe at down to 2 pounds or so. The instructions are listed on another web-site (complete with drawings to show the amount of engagement required), and if you need the address to take a look see, shoot me an e-mail.
Larry