I spoke with Wilkinson about this and he said the pilot ball bearing pretty much has to work correctly. This makes sense because it is already in use by a bunch of GT40s. He also explained that the needles in a pilot needle bearing are hollow and softer material than the ZF input shaft and when it fails the needles disintegrate and leave the input shaft unharmed. His only concern with the pilot ball bearing is that if the ball bearing seizes then the input shaft could spin on the inner race and it could damage the input shaft because the race is harder material than the input shaft.
My hunch is that the pilot ball bearing almost never fails. The needle bearing is more likely to fail because it is unsealed. Either bearing gets very little use in our cars (Panteras and GT40s) because we don't drive them that much and they are only behaving as a bearing when the clutch pedal is pressed down.
Just an aside, he also shared that he has pulled a lot of Ford oilite bushings with oblong holes. This likely applies to Panteras that had been driven 50,000 miles or more.
He can still get the Ford FC65662 Pilot Needle Bearing and received his last batch about 6 months ago.
I canceled my order for the ball bearing from Amazon. Wilkinson said he can get the ball bearing for $4.