I am not very familiar with Dodge, I usually spend all my time in the Jeep forum. I found a '72 Dodge D200, 4 door, 4x4. Its got dana 60's and a cargo box, its the type of truck Caltrans or PG&E would use. My question is, how do I tell what motor came in it? I know the options are 318, 360, 400, 440. How do I distinguish between them? Also, if I can get the VIN #, is there a website where I could decode it?

The 318/360 will have the Distributor in the rear.. The 400/440 will have the distributor in the front however I do not think they were available in trucks till 75.
The 318 can be distinguished from the 360 by the harmonic balancer.. The 318 will have a smooth balancer while the 360 will have an oval shaped weight on the front of the balancer right behind the pulley.. The displacement will also be stamped into the block just under the head on the drivers side.. The displacement is also cast into the drivers side of the block..
The 400 will have an extra weight on the balancer like the 360 and will most likely be a 2 bbl.. The 400 also has a machined pad on the drivers side of the block which is even with the bottom of the head and will be stamped with the displacement..The displacement will also be cast into the side of the block below thw head..
The 440 will be a 4bbl and have a machined pad below the distributor on the passenger side which will have the size stamped in it..Also the machined pad on the 440 will be about 1/2 inch below the bottom of the head instead of even with it like the 400..

Cool, thanks. Its pretty easy when the numbers are cast right into the block isn't it?