Welcome. Your English is a lot better than my Swedish.
Your model number is written like this 1-6231.
Pto's were optional at the time. The model 8-3311 fit the 1" shafts and the 8-3111 fit the 1-1/8" shafts but both were Kohler engines that used a ball bearing on the crankshaft that would withstand the pto pressure. The manuals for both are in the Files of
http://groups.yahoo.com/group/wheelhors ... rmanuals3/They are named "Pto Engine Manual 1968 8-3311 #A-5167" and "Pto Engine Manual 1968-69 8-3111 #A-5169". I think the clutches are the same. The difference is the ID of the inner race for the large needle bearing.
When Wheel Horse used a Briggs and Stratton engine they added a ball bearing so the same style of clutch could be used. They did this on the 81-16B801 (1978 C-161 Twin 8-speed) and 01-11B803 (1980 1100 Special 8-speed) plus many more. There is a product service bulletin on how to preload the bearing when installing the pto clutch. It can be downloaded from the Files of
http://groups.yahoo.com/group/wheelhors ... rmanuals8/It is named "WH61-90 #326B PTO Thrust Bearing Preload"
There are other pieces needed to mount the bearing and you can see one of them in the parts lists for the 01-11B803 model at
https://lookup3.toro.com/partdex/index.cfm?xCaller=ToroOpen the engine parts pages. The bigger engines used a different plate or a ring but I can not find a picture of it.
The early 1968 production of the 1-6231 Raider 12 used a Kohler engine with a combination starter/generator and battery ignition. The later production used a Kohler with Bendix starter, alternator and magneto ignition with points and condenser. The tractor's model number did not change. The manual for this late model is in the Files of
http://groups.yahoo.com/group/wheelhors ... anuals1_1/It is named "Tractor 1968 Raider 12 Late 1-6231 OM #357 -1" and there are 2 different copies of it there.
Let us know what you figure out.
Garry in Canada