The "O"s sleeve hitch was made completely different. The "arm" on it angled up, whereas all others came down. Sleeve hitches aren't all that hard to come by at all. Put up an ad in our "Wanted" section or check with the sponsors above.
Here are some pics:
"O" sleeve hitch (incomplete assm):
O sleeve hitch.jpg
Sleeve hitch for a 73 (complete assm):
(The lifting section is upside down)
sh73.jpg
I buy a lot from these guys and they have one for a 73 in stock:
http://ihccw.com/sleevehitch.html