Welcome John
Sounds like you have a great 53 3600. I love 3/4-tons. Please post some pictures in the gallery. Your old, tired 216 can relatively easily be replaced with a later, better 235 or 261. It's almost bolt-in as Cletis mentioned. There's really no reason why you can't drive it 55 mph now, as-is - if steering, brakes and tires are all good. As far as upgrades go, don't make it go faster than you can steer and stop it. Do your research, take your time and plan before you take it apart. Good luck.

Professional Novice