I had a '66, a '71, and a '73.
The 66-67 splits had a 1500 motor that will get you up to 60 or 65 on the flat. I never had trouble with the transfer cases. I think '71 is the best year of all. 1600 dual-port motor and disc brakes. Older and you get the drums. Newer and you get the troublesome pancake motors.
"Can they be made safe?"
Absolutely. Don't drive them.