On a straight opener swap in a house from this era, the first thing we check isn't the opener itself but the receptacle it plugs into. A garage built around 1968 almost always has a single, non-GFCI outlet near the header, not the two-outlet GFCI-protected circuit current code expects for a new install. If that circuit isn't there, bringing it up to code is part of the job, not an add-on we spring on you later. From there it's removing the old head and rail, mounting the new rail and bracket, running power, installing and aiming the photo-eye sensors, and setting the travel limits and force settings so the door reverses correctly on an obstruction - that last step is the one DIY installs most often skip, and it's the one that matters most for safety.