If the lobes are shiny and not blue it’s fine. If they are blue it’s not fine. You turn cast iron blue and it’s been way too hot.
There is more to an oil than ZDDP content. Too much ZDDP isn’t good either because it affects how the oil is built.
Never use an additive because of the above. Some Tribologist spent a bunch of time selections each component for that oil in the specific percentages used so all of the other additives like the detergents, dispersants, anti foam, viscosity index improvers and such all work together.
Using an additive can, and probably will affect how the other components function. Too much of one thing (such as ZDDP) can change how one of the detergents works.
If you have to use an additive buy a better oil.
Unless your bearing clearances are from the 1970’s there is no reason to use a 50 grade oil. Chose the winter grade number based on the lowest ambient temperature you will see and the grade number based on your clearances.
There is no good reason to run bearing clearances as loose as was used in the 70’s and 80’s.
Also, if the builder used full groove main bearings and a standard pump I wouldn’t be happy about that. You can use 1/2 groove bearings and a standard pump, but not with full groove mains.