Update - one of the experts (in fact a very senior ex-Boeing engineer) has theorized that this was a wing fire, not an engine fire. The area which can be seen to be on fire in the photographs is at the rear of the left wing, between the two engines. He notes that there is a fuel manifold here, with many hose connections, and that in this area is an electric wing flap motor - so that a fuel leak here could lead to disaster. The flap motor would likely have been used as it was shortly after takeoff.
The pilot put the plane down perfectly, on all three wheels, but the fire could not be put out and eventually consumed the plane. I have a series of photographs but cannot post JPGs here - but it is obvious that the pilot did not crash it; he made a good emergency landing in the field and it just burned up.