Torque Monster !

Marine engines work mostly at one rpm, governed by the propping . And they have water-cooled manifolds. You might be able to get away with wide seats in that marine application, but
would you have much success in an engine that is gonna see many and diverse throttle openings? I think you would be better off controlling cooling in the usual ways. IDK, I'm just thinking out loud.
But cruising at just 2400, the exhaust valves will have plenty of cooling time..... especially if you can figure out how to get the mixture to all burn in the chambers, beginning with providing an early enough spark. That's gonna be key. If your mixtures are still burning on the way out and into the headers/logs, that is gonna make it tough on the exhaust valves. And you cannot attack that with seat-width.
If your engine will want (and I don't know that it will), Cruise-timing in the 40 to 50 degree zone, that is gonna be a lil tough to provide, with a normal mechanical curve plus the Vcan. So expect to do some learning the D.
Have you cruised it at 2400 already?

by any chance, can you post a pic or two of that unit? I'm wondering what you actually have, and how heavy it is. And most of all, how it presents to the wind.