Derk
I think the notch on the handle shown might be to lower a hydraulic jack as opposed to being for adjustment of the carrier brakes. That said, it would be awkward working with a notch in the handle like that. But if it is hard to work the hydraulic jack release valve, imagine how hard it would be to get quarter turns behind the backing plates in the tight area behind the axle armour protection plate.
As Colin mentions, the 17801 will be the group number from Ford for jack handles as opposed to a part number specifically. There will be letters and or numbers (or a combination, depending on when the prefix was initially created) denoting what vehicle the item was originally designed for, along with a suffix denoting changes in the item.
There is one of the handles ( 78 17801 ) with the commercial number currently on ebay. They come up regularly.
https://www.ebay.com/itm/31361427490....c100667.m2042
Knowing Derk, he will not be happy with the commercial handle though, as it is too easy to get. He will want the military handle. I am attaching a photo of the track jack in use to compress the springs. Note which handle is in use. Yes, it is the 78-17801.