Timing chain breakage is very rare in these rigs. Even at 300k+ the problems usually seem to be either headgasket, PHH (heater hose at the back of the head) and birfield/cv joints.
You'd be better off checking on the headgaskets and the heater hoses. Go to
IH8MUD.com - "The Truth is in the Rocks" and search the 80 forum for "phh"
You can check the cv joints by driving forward with the wheels turned left then right. If they clunk-clunk-clunk turned either way they could use some attention (but you'll probably be okay if you're going to keep the truck on-road all the time).
-G
Former '94 FZJ owner