Thanks for the replies!
Tried the mirror, and I think it is torx, but that won't grip either (probably hasn't moved for 12 years). On the V6, there is no way of getting a vice grip on the second bolt, because of accessibility. The first can be got at, but it's a domed head - how would you grip that?
I've now got a CEL which points to the MAF sensor being the problem, so the urgency to move the cam sensor is gone, but if I need to change it, maybe the engine would have to come out!