Theoretically, when the engine begins to cool there is a slight low pressure zone within the cooling system due to PV=nRT. That is with respect to the crank case. This is one of the reasons why there is an overflow for the cooling system. Coolant is forced out because of pressure and returns upon cooling.
With a severely damaged LIM I guess it is possible to get some oil in the cooling system. Although if you think of it logically the lifter valley is far below the LIM gaskets. The lifter valley would have to be quite full of oil to get any appreciable amount of oil into the coolant system in this manner.
It's more likely that when the motor is hot you'll get coolant in the crank case which is what most have observed. Coolant is forced out the leaking LIM gaskets and into the lifter valley.
You say 95 Delta 88. Maybe the Series I is a little different. I worked on an old Buick LeSabre with the Series I and it looked quite similar to the Series II.
