Those are technicaly grub screws, though they do not appear to be the normal type for that job. One of the screws should be directly above the key, so it is pressing the key down, which I think is what you said.
If you back out both grubscrews, the clutch should only be held on the crankshaft by friction. Once you unbolt the engine from the mower deck, fairly gentle use of a lever between the crankcase cover and clutch boss should push the two apart.
