In general, all Ford Motor Co. part numbers are descriptive and have other meanings. The includes Mercury products. The "W" is the indicator for an item (part or assembly) that was originally designed by the Mercury Cougar. The correct part number should have a "0" (zero) instead of an "O" (letter O), which, with the "D" indicates an item designed for first use in 1970 ("D" = 7). Some numbers actually defines the item, and that is important to verify what it is. The "B" is a Body engineering design. So, to verify what you have, the entire number should be used. There are quirks in the system, so don't be intimidated. Two of my Mustangs use Comet designed distributors.
In answer to your question, a D0WB would be a good indicator that it is a Cougar item. The rest of the numbers would confirm this.