Hatch installation advice
I have a '78 H33 which for all intents and purposes is a slightly strecthed 30. My boat came with a hatch where you describe but it's not quite as big as what you're looking to add. I have a couple of tips/corncerns to relay. First, with a big hatch will you still be able to open the companionway hatch fully. Second, if you plan to leave the A/C in place while sailing will lines dangling from the boom pose a problem. Lastly, if you do any work on your deck, especially on the coach roof, be sure you seal the balsa core with epoxy around the cutout. Good luck.