The Polaris 800 went to a powervalve about 8 years ago and has never looked back, gained power across entire ranges.
These cylinders which are between 2002 and approx 2006 will most likely be the ones he uses because:
They have a modern port layout
They are non dfi
They have powervalve, one of the best non servo based valves you can get!
The stroke matches the cr stroke better as its only a couple mm shorter (hence the 30cc gain). Whereas the next later model had a short stroke and ones after that went dfi
I was / am looking at putting one on a bighorn 350 bottom end so did my tease arch on the Polaris 800 efi cylinders.