If you are dropping a stock 1970s turd in, no its not worth it. If you put a good mild 302 in you'll like it. Most likely you will grenade the 7.5 rear. As far as how hard, it depends on your skills, the drivetrain you want to use and so on. If you are pretty witty, you can do it with basic tools, a drill, grinder, and without a welder. I did a basic swap with a mild 351 at first and pulled it for the stroker I have now. I'm pulling that as soon as the combo listed in my sig is ready.
Matt