There are a pair of pan head screws that join the side cowl vent and the operating handle. I have removed two. However both were removed from cowl panels that were removed from the cab, so there was less interference behind.
One will be accessible with the vent open. The second may require developing some sort of custom tool. I had considered using a screwdriver bit on a 1/4" ratchet with a long handle.
Once the screws are out, just wiggle and jiggle until they come apart and out.
Of course, its a flathead, going to be rusty, and stuck. So best of luck, hope that helps.
