Unless the seat is cut very deep, there would be no reason to install a new seat. If just a little deep with a stock valve, a slightly O/S head diameter will put you back in the black. Search for a resent discussion on seat installation for opinion. My personal experience and observations suggest that installing seats in flathead cylinders just doesn't work well.
I'd use a "Bowl Hog" to narrow the seat and use over sized valve but dont go to big or deep so if you ever do go the replaced seat route your not in trouble.
Bowl hogs are just steeper cutting seat cutters. Look over at Goodson.com
PS: I think the seat post was in 45 flaties
Just talked it over again with the guy who's gonna do the machine work. And now he said that it was'nt gonna be a problem fixin the seats without using inserts! Maybe he just wanted a little extra work...