I found a little history about these tractors online with a Google search.
"Although this is an old ad I thought I'd respond. The WorkBird was made by the George Tools Division of Community Industries in Sullivan ,Il. They were in business from 1946- 1966 then bought by Montgomery Wards then Yardman then MTD and then the plant was closed by MTD. The management/employees/and others went on to form Agri-Fab within 6 mo. of the plant closure.The WorkBird was way ahead of it's time and would have been a great product for the late 90s thru today.With it's basically zero turn capability, up front cut and add on accessories it would survive today but at that time nobody was ready for such a machine.Parts are virtually impossible to get except as with most all machines the engine parts. The Vintage Garden Tractor Club of America web site has manuals for sale on these units. Hope this helps! Gary"
I found this at, http://www.yesterdaystractors.com/gardent/messages/55304.html.
I have since emailed Gary, the author, and he seems to have a good deal of knowledge about these tractors.