Another interesting thing to point out is this particular pump's gear rotor is not exactly the same as the patent diagrams. If you read whats actually in the "claims" section, there is no mention of number of teeth or shape of teeth which is something where they differ. There are several other slight variances between patent and actual implementation that could possibly be the result of whats done for different size pumps and/or subtle improvements or reductions in cost through the years. It could also be places where a generic and brand-name walbro could differ.
It seems the "Walbro" name may be on a similar track as the "Westco" name. Both used to be a company name, but now almost more appropriately refer to a type of pump design, that without patent protection, is easy for just about anybody to manufacture.
Here's a link to a Westco style, or "Turbine" pump -- its not a fuel pump, but the PDF has an informative breakdown of the guts of what makes it work.
http://www.mepcollc.com/1484.pdf