Too many things can cause coolant in the oil. We need to find out if this is happening under pressure or not.
Drain the engine oil completely and leave out the drain plug. Fill the radiator with water and leave the radiator cap off. You do not need to run the engine at this point. Look for water coming out of the oil drain. If you start seeing water from there, then we need to find at what level in the engine it may be coming from.
Find a hose or water jacket plug below the cylinder head, as close to the block deck as you can and remove it. The water above that point will drain externally. Once that upper area drains, see if you still have water coming out of the oil drain. If you do, then the problem is in the area below that point which is normally a liner seal. If it stops leaking, then you will have a leak in the cylinder head area or above. Leaks above the block deck on 53 series engines are usually a rolled oring in a water jacket under one of the cylinder head which is a common problem. The perimeter seal will catch the water leaking and put it directly into the oil pan via the oil drain passages in the engine block.
If you can get this far, then there are other methods to check for injector tube, cracked heads, etc.....