My son drove his 89 Nissan pickup until it started “clicking” and the oil light came on and it wouldn’t start. Four quarts of oil later and a jump start got it to a AAA shop who said the “high knock” is OK but the “low knock” is bad and it needs a new engine. Sounds like rods and bearings?
No knock is acceptable, high or low, and considering what happened the engine is no doubt trashed.
Considering the age of the truck it would be better to try and find a decent used engine and swap that in if he is going to keep the truck. A proper (key word) engine rebuild can get very expensive.