SAE30 in all 71 Series DD engines
SAE 30 was the DD recommendation for a long time , but the eventually found better life at 40.
Hound would change (rebuild) engines mostly by time , although the goal was to swop em out at about 200,000 miles.
A friend was a wrench in Miami , way back, and claimed a 4106 swop would be done by midnight by the night shift. Only realigning the Air Cond was left , as that took a long time.
This was back when 5lbs of freon would be added each week , and was considered a tight system!
They started with the replacement engine and tranny already mounted in its cradle.
Thank goodness for Cannon Plugs!