Actually the book author is Don Bunn, and he has published several books on Dodge trucks. The one you want is called "Dodge B-Series Trucks, Restorer's & Collector's Reference Guide and History". It has a lot of great information on our trucks.
As for originality... that all depends on what you want. My truck is mostly original and I enjoy it. Mark's (ggdad1951) truck is about as original as any I know and it is awesome. I also know of several that are modified and they are very nice too. I don't know that either way detracts form it's value.
As for "Numbers Matching", the only numbers that seem to count are the engine number (stamped into the block just above the generator) and the chassis serial number (on the ID tag on the left side A pillar, and stamped into the frame, left side near the front axle). Often times the title is registered to the engine number, and the engine has been replaced with something else over the years. This can create some issues with the DMV.