If it was made in 1991 it is a 1991 or 1992 model. You can order manuals and download others from
https://lookup3.toro.com/request/request.cfm1991 Model 31-16O803 Use 1012345 for a serial number. (16=hp, O=Onan engine, 803 are all numbers)
Also try model number R1-16O804 and 2012345 for a serial number. Forgotten why I added this 1992 export model in my notes for the 1991 416-8.
1992 Model 31-16O804 Use 2012345 for a serial number.
To determine the model numbers of your attachments go here
https://lookup3.toro.com/partdex/index.cfm?xCaller=ToroEnter the tractor's long model number and the next page has a link to the list.
The are a few product service bulletins listed in the largest Database Table here
http://groups.yahoo.com/group/wheelhorsetractormanuals/Do a search using the tractor's long model number. The PSB's are all in the Files of
http://groups.yahoo.com/group/wheelhors ... rmanuals8/Garry