Hmmm. Bugger. Although, if its that close to the main hoop, is that going to cause an issue in getting it logged? Seem to remember something about 150mm minimum distance between your head and the main hoop, although no CAMS manual on hand.
Not sure about log book. But there is actually no where else to fit a cage and a seat, so we'll have to see what happens. Might modify the mount to get log book then put it back. The rear hoop sits BEHIND the seat, so you aren't going to hit that, and the bar along the roof is padded, so that is not an issue. Basically, to hit exposed hoop you'd have to snap the seat. In that case, hitting the hoop with your helmet is not #1 priority....
You can see the clearance here sort of:
Note that the seat sits forward of the main hoop.
Maybe this is a slightly better photo?
Not home at the moment so I can't just duck out and take one.
I think I found the seat I'm after. The suggestion of the Cobra seats got me looking and I found the Cobra Suzuka Pro. It's a Fiberglass/Kevlar frame instead of straight Fiberglass and is slightly smaller than the Sparco's.
$1200 from revolution racegear, or $750 +shipping from the UK