I don't know what you mean by a 'surge lock'.
Some more description is needed to know how much oil to use. You say it is 50° so I assume it is in a Vanagon. There is not any factory spec for a 1.9 in a vanagon installed @50° because they were never installed stock. Because of that, any quantity is a guess. 4.5 quarts is usually fine unless you are also running an auxiliary oil to air cooler in which case you need to fill the lines and cooler also. That amount varies depending on the install. One thing that I have found on multiple TD/TDI vanagons is that if the level gets low then when you transition from cruise to acceleration, if you watch the boost gauge, the oil pressure will drop or not increase as linearly relative to RPM. This is especially obvious when the engine is cold. Just above where it does that is just right. You want to be above where that occurs.