Re: mauser truck gun build
My favorite truck gun is a 243 win with a 20" bull barrel. It works great to carry around in the feed truck for coyotes. When I think truck gun I want short overall length. I carry my 264 on really windy days but the 25" barrel and long action make it inconvenient. Another thing I want on a truck gun is a 3 position safety. I carry the gun with the chamber empty, but like to be able to lock the bolt closed.
What are you planning to shoot with your truck gun? If it will be used primarily for varmints/predators I wouldn't go bigger than at 6.5mm. A 6.5-06 or 264 win would be a good choice with high BC bullets for windy days and moderate recoil. Either would need a 24" or longer barrel though. Another good option would be to build a 243 or 6mm on the long action so you could seat VLD bullets out long. I wanted a 6mm-06 but my gunsmith talked me out of it, he didn't think the barrel would last with the amount of shooting I do. Decide how you will carry it and how long a gun you want to deal with.