Tom Hoel wrote "The Civilian M60 Machinegun Owners Guide" in 2003. It originally appeared as a 6 part series in SAR in the same year. It approaches the ownership of a M60 GPMG from a civilian's point of view, detailing how it works, how to treat it and what to do when something breaks.
It's being republished by the author on machinegunpriceguide.com. Currently it's a work in progress of text with no images but can be accessed directly only via the link http://www.machinegunpriceguide.com/html/m60_part_1.HTM
It will answer many questions of how the transferable guns were made and which are the most (and least) desirable.