The 16 in the 10-digit Kohler serial 1630007643 makes it part of Kohler's 1986 production.
Wheel Horse used the spec. number 461521 1987-1991. The 1987 Wheel Horse product would have gone into production prior to October 1986 because that is when the new models for 1987 were introduced. It's a pretty safe bet the model number of your tractor is 21-10K804. The 1st 1=garden tractor as opposed to lawn tractor, 10=hp, K=Kohler engine, 8=8-speed transmission, 04=parts list identifier.
Not aware on an online operator manual for your tractor but the parts lists are herehttp://www.partstree.com/parts/
Type Toro in the 2nd box and the 21-10K804 model number in the 3rd box. The parts that are still available from Toro are priced.
You can get to a list of the attachments and their long model numbers herehttps://lookup3.toro.com/partdex/index.cfm?xCaller=Toro
Enter the tractor's 21-10K804 model number and the next page has a link to the list.
You can order an operator manual and download others fromhttps://lookup3.toro.com/request/request.cfm
Enter the 21-10K804 model number and type the word none in the serial # box.