And I don't think 50636 is a nut. In the pic its more in the position of a bushing, or weird washer, which I've never seen. And the part number is not in the AMK Guide to Ford Fasteners.
The drawings I've seen call out a jam nut, 33924, but every top I've seen if the serrated flange nut you show in the photo. I think it is 55738.
- Nut (x1) – Ford part #33924 (pg 180)
o Hex Nut, Jam, 3/8-16 thd, .210/.227 thk, 9/16” hex
o Note : This appears incorrect. Most tops I have seen have a flange nut, more likely Ford part #55738 - Hex Flange Nut, 3/8-16 thd, .346/.363 thk, .771/.793 OD. 9/16” hex
AMK sells one real close.
http://amkproducts.com/bulk3.asp?part=B%2D12900(image from AMK Products website -
http://amkproducts.com/default.htm)