I currently use a Quarq S975 compact powermeter. Has anyone used a compact Quarq on a Scott Foil? Is there enough clearance around the BB shell?

Quarq has a list of known fit issues on their website.
Have you checked there?

My S975 Quarq rubbed slightly on my Addict R1. A little sandpaper did the trick.

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2013 Wilier Cento1 SR || 2009 Ridley Crossbow || 2011 Yeti AS-R 5 Carbon

I just installed an S975 on my Foil Team yesterday. It fits fine. I thought the magnet was going to be tricky, and got some double sided tape to test positions before going with the epoxy they provide. The chain guard is magnetic though, and the magnet just flung to it, and it turns out, with one magnet the position is fine and the Quarq functions. I've only done the trainer, but it seems like a pretty strong bond and I'll probably just leave it.

I've installed both the old S975 and new red quarqs on foils of various sizes with no issues whatsoever. There's tons of room.