Here is an early AF-2W in Grumman flight test (it is configured with an ejection seat):
Here is a Navy Reserve AF-2W:
My post on the AF Guardian (HERE) failed to note that. I overlooked the obvious yet again.
I have no idea when or why the change occurred. It appears to have been a production change as evidenced by this picture of BuNo 124783 on the Grumman flight line.