rather than replace it make it dual purpose
Rather than replace the cowling in the anchor locker with a hawse pipe I would keep it is as a colwing and make it so that it can be a hawse pipe.
Generally I install Bronze threaded deck plates, purchase the cowling that fits them, and an extra cover. The extra cover has the center removed to be the hawse pipe, insert.
When at dock, the cowling is installed, and the chain and nylon stored below in the anchor locker. At sea the deck plate is threaded in to prevent water ingress completely, having tried everything from modeling clay to nerf balls, I can report that the only thing that works 100% of the time is a threaded deck fitting. When I go to anchor I insert the cover plate with the middle cut out, and run the chain and or nylon through it.
When you want it closed off you unscrew the modified center, and screw in the full o ringed cover plate. That way you don't get any water below.
You can even do a variation on the threme using the cowling vent if you are anchored in a nice quiet anchorage, and don't have an all chain rode. The nylon just comes out of the cowling and out to the anchor.
Guy