Hi Björn !
Here the answer is:
When your motor is completely restored (new bearings, cleaned oil system and a paper oil filter) you can use a 20W50 oil with additives (dispersants) to get all metal fines and carbon transported to the paper filter.
When in your motor the original oil filter is and you don´t changed all bearíngs and not cleaned the motor oil system completely you should use an oil without dispersants. (SAE40 or in Winter SAE30). In this case all the fines and abrassives falling down in the sump. This is OK, because otherwise your dust will be solved into your oil and is pumped allways in the oil circle to all lubrication areas. This will have negative longlife of your bearings, pistons aso.
Without a paper filter you should clean your oil sump with every oil change.
Happy new year