II'll stick with non-detergent 30W in old motors I do not know what has been used for oil in the past,just in case they were run on it all along and are sludged up--it would do much more harm to use a high detergent oil in such an engine and loosen all that dirt and crud up and send it throughout the motor..
We "killed" a few nice running motors in antique cars we got running ,by using multi-weight detergent oil in them--soon after we changed the oil,they started clattering,the lifters first--then they started smoking badly,and a couple of them seized up..bet they would still be running if we had used non detergent oil..sometimes all that sludge is all thats sealing the rings and seals up!..
But I always use detergent 30W,or 15W-40 Diesel rated oil in engines I know are clean inside,if I have had them apart and cleaned them good inside..when there is NO oil filter,its imperative to keep it clean!..how air cooled VW's lived with just a screen for a filter,and having only a 2-1/2 qt. oil capcity baffles mee too!--just about every one I did oil changes on looked like they had roofing tar in them,not motor oil!..yet they seemed to run forever anyhow!..they reccomended straight weight oil too,adding multi-weight oil to an old VW usually resulted in regret..