Sir George,
WRT helmets in the Grob, it's not really an issue. I've flown both with and without helmet (mil and civvy G-115) and to be honest I actually prefer it with a helmet, it certainly doesn't restrict lookout.
From the findings, and the reconstructions used, it looks like an unfortunate case of "same way, same day, under a wing/nose to each other" with the addition of airspace considerations bottling people into a specific area.
Unfortunately those factors led to the loss of two really nice blokes and two young ladies who I'm sure would have gone on to bigger and greater things.
Two's in - This is the MOD, it still takes me half an hour to check my email (which I can only do from work)