If you can get your hands on a copy of the George Putz book on canvas covered boats he shows one of his 18 1/2 foot Walrus designs with a rowing unit installed. The rowing unit, consisting of a sliding seat and outrigger mounts for the oars, is available separately and (according to Putz) can be used in other boat designs as well. The name and address of the supplier are in his book. Sadly I don't have a copy nearby or I'd post that information.

I believe Glen-L and/or Clark Craft sell plans and/or parts for building your own rowing seat and oars.

Putz spends a few paragraphs on the minor modifications to the cockpit shape and size so the rowing seat unit can just drop in. You may be able to glean some information from this which might help you. I believe it can be removed rather easily so the kayak can be paddled if you wish to face forward.

Good luck with your project

Paul G. Jacobson