For reference, the defining difference is at the base of the sweep, where the hinge attaches to the center. The "narrow base" sweep is 16" measuring from the end of the hinge pin across the sweep to the end of the hinge pin on the other side. The "wide base" sweep is 22" wide. That extra 6" will tell you beyond a reasonable doubt which sweep you're looking at, even if you don't recognize the other differences in the way all the gussets are welded on the sweep. Once you've looked closely, you can easily spot the difference from about 30' away.
I can't speak for the NDT requirements. An old bulletin actually states that a visual inspection of the sweep at a couple of key points is recommended "at each set-up or every seven days of operation". Again, I don't know the current requirements, but I understand that while the narrow sweeps are known for severe cracking, as of about fifteen years ago there had never been any cracking in the wide base sweeps.
I would consider "not known to crack" vs. "known to develop cracks" to be a distinct benefit, but that's just me. [8d]
Oh, and remember...my word on this is worth exactly what you paid me for it: I'm not claiming any expertise here.
--Dave Althoff, Jr.