Rad/Grille Winter Cover
The winter cover will help to warm up faster and stay warmer in -40s and provide you better cabin heat. If you find a lack of cabin heat at highways speeds that is the real reason to install one. Around town on shorter drives, maybe not necessary depending on conditions/your temp gauge.
If you are able to use the block heater, that is a complete bonus for start ups as it no longer takes 15+ minutes to reach normal temps and obtain full cabin heat.
I am sure you already know that synthetic oils throughout the engine and diffs etc are advised and recommended for -40.
When ever it is clear and cold, I plug in a 120 volt GM car warmer and keep the interior slightly warmed,to tolerate the interior when I get back in.
If it is snowing I will not run the interior heat as it will ice up doors windows etc.
My old Car Warmer:
http://farm4.static.flickr.com/3072/2823188743_79c655a777.jpg?v=0 and it still works.
For the grille I made my own cover made out of 3/4 "felt hair pad (covered by Naugahyde) and used zip ties to attach. It isn't pretty, but it works to keep it somewhat toasty. Now how about some insulation in the floors and doors!