The gores on either side of the slit have no need of an adjoining rib so these nearest slit can simply be left out. Though the opposite side of the adjoining gores will still have a normal rib which stops at the slit framework. The two gore's horizontal struts can be carried right over the intervening inch to stop at the slit framework. To be fixed there as if they were normal ribs. Though the miters on the slit end will be at different angles to normal ribs.
It would be safer to match the slit framework to the complete dome skeleton to ensure geometric accuracy. The top of the slit can be left square. Or a rounded collar could be formed from laminated plywood glued in enough layers for adequate strength. Weatherproofing at the zenith is obviously important as any leaks will fall directly onto the mounting or telescope, or both.