I think 3 plugs is all there is. There is one toward the front, right in the center, and the there is one off to the left on the lower part of the housing. This one would be where the sump for the lump pump would be if the rear end had been used on a 1655. The last one faces the rear, at the lower right hand corner of the housing, below the PTO unit.

The read end and transmission are open to each other, so it is all the same oil. But there is a wall that separates the main transmission from the final drives, and that wall keeps a certain amount of oil in the front compartment, that's why there is more than one drain plug, even though it is all the same oil.