I am starting a new topic that deals with the different types of PTOs.
I have a 1970 accessory catalog That list a front PTO that bolts on to the front of the Original, 70, 71, 100, 102 & 122 Which has bevel gear drive unit(like snow blowers and tillers use) which has its own clutch and can have a pulley or a spline adapter available.. The price was $64.05 for Original and $61 for the rest. I have never seen one of these units but I do have a 1/1 ratio snowblower bevel gear box I am going to make one for my Original.
The rear PTO is listed for Original( $42.28 ), 70, 71, 72, 73, 100( $42.28 ), 102, 104, 122, 124( $42.28 ), 106, 126( $60.50 ). Each group has its own part number because of the different mounting ans engagement lever as Paul Bell noted. I have a fake PTO in my Original as I can't find an Original main shaft.
Sorry for the smileys
I also have a wheel PTO that was marketed by some one but they are easy to make. I never saw any ads for these wheel PTOs which use the wheel weight bolt holes to mount. I have heard of these running elevators. I use mine to run a screw type log splitter that was an IH approved option made by Unicorn.
I run a Mott flail mower on the front of my Original that has a clutching system and I do take the belt guard off and run a furnace blower on hot days at shows.
I sure wish I could post pictures as it takes a lot of typing to explain a picture. I would appreciate any other information on PTOs that you may have. Thanks