I will respectfully offer my opinion regarding adding heat to the 6.2. There are other threads which discuss adding heat to the larger engines, however my comments pertain to our CUCV engines.
Having owned and operated diesel engines for over 40 years, first with construction and grading equipment and then with my personal vehicles beginning with a 1985 K30 truck, I have come to some conclusions in regards to cold weather starting. Years ago I used freeze-plug type block heaters exclusively for starts in cold weather. These worked great for my front end loader and larger trucks. While these indeed improve starting by inducing BTUs into the engine block, which is essential for diesel fuel combustion, they do nothing regarding oil viscosity when installed in a 6.2. All engines have oil pans, and all excess oil throughout the engine drains to the pan when the engine is shut down during nighttime. This oil then sits in the pan and cools to ambient temperature and stays that way until the engine is started in the morning. Even with freeze-plug block heaters and/or tank-type heaters, which keep the engine block warm (or warmer than ambient air), the oil in the pan stays at ambient temperature. All motor oil produced from natural crude decreases in viscosity on a sliding scale equal to temperature. The colder it gets, the thicker it becomes. And the thicker it gets, the more difficult it is to be pumped (by the engine oil pump) up through the oil passages. The CUCV TM recommends 15w40 oil. What this means is, at a normal engine operating temperature of 210 degrees, the oil will have a viscosity of 40. At colder temperatures, the oil will have the viscosity of 15. What is unclear is, "How Cold?". There is a good article on this subject at
http://www.upmpg.com/tech_articles/motoroil_viscosity/
I now believe it is more important to warm the oil in the pan than to warm the engine block, or better yet, to do both. There are currently available three different methods of warming the oil in the pan, 1.)- dipstick heaters, 2.)- magnetic heaters which are manually attached and removed from the pan, and 3.)- a heating pad which is permanently attached to the exterior surface of the oil pan at the lowest point. Although I have never used a dipstick heater, I have heard and read comments that these devices are not very efficient and do not add sufficient BTUs to the oil, especially during extremely cold temperatures. Consequently I would not use this type. The magnetic type heaters work excellent, however they are somewhat large and must be manually attached and removed by hand, which means you are going to be laying in the snow or on a cold ground twice a day to use them. The third type, and the type I plan to install on my M1028, is the heating pad that is permanently attached to the oil pan. I plan on installing a Canadian Polar Pad on my oil pan, transmission pan, and transfer case, and wire them all together
http://www.canadianpolarpad.com/installation.html . I have used these pad heaters in the past with excellent results.
In summary, I believe the best (and least expensive) setup to assure quick and safe starts in cold weather is to install the Polar Pad and 2 GM OEM freeze-plug heaters, one on each side of the engine. Just my 2 cents.
Hope this helps.