Break up cowlings again and install them, and do some measuring for a plenum. I am following the Jabiru plan and covering from the baffling attach face on the heads to the most inboard cylinder cooling fin, minus one. I mocked up the biggest area I could over the starboard aft cylinder, and allowed for about half of that area over the forward cylinder, tapering back to match the cowl exit, bending to miss the starter ring gear. I am aiming to make a form to create the sides, top and front, and do the aft bottom later.
First hack at a cooling plenum form
Leading edge of same. I did try it with the baffling