Hesse upper - ok, you got one of the worst ones there, sorry to say - but no biggie if it runs reliably. The W isn't what I was talking about but anyway - those are the feedramps and it sounds like it's what we call the Widow's Peak configuraton, which is good.
CAI - Century Arms Int'l aka the Angry Beavers - another bad sign, but again, as long as it runs reliably, that's all that matters (personally, I'd have the headspace double-checked by a competent 'smith). Century threw together any combination of kits and receivers - metric receivers onto Inch kits, etc so we need to probe a bit more.
What I was referring to earlier is a bit lower down inside the magazine-well itself - the cutout for the magazine lug. Metric mags have a little dimple punched-out in front, Inch mags have a big ol' rectangular steel lug welded to it. I'm not aware of Hesse making Inch receivers, so I'm assuming your mags have the small dimple.
As for the rest of the rifle, what are the markings for the selector - S, R, A? Any serial-number on the lower receiver? The gas-block ears (protecting the front sight) - are they solid (closed-eared) or do they have a big hole through both sides (open-eared)?
Also, describe the rear-sight - does it fold down flat or just slide up and down a ramp (or something else)?