Here's our 2 cents worth...
Daedong diesels are indirect injection diesels. In other words, preliminary fuel combustion takes place in the pre-combustion chamber in the head. The glow plugs fire directly in the pre-combustion chamber (800 degrees is 4 seconds). This is what helps the diesel combustion in cold temperatures. From our experience, a properly operating glow system will allow the tractors to start even in extreme teperatures. May take a couple glow cycles with the auto systems, but 99% of the time, the engine will start.
So..it's been our recommendation that if you want to assist the engine in cold weather, warm the oil. Since the glow system is there to heat up the pre-combustion chamber, warming the oil for circulation at cold start should be the focus on in-direct injection diesels. We have installed radiator and oil pan heaters when requested, we have not installed block heaters. Our hesitation with block heaters is the ability to "dry" the cylinder walls. By warming the block, the residual oil on the cyclinder walls warms and runs faster than it would cold. Block heaters may be the best solution for a direct injection diesel, it's been our position that it may not be for an in-direct injection diesel.
Just our approach.