Just out of curiosity....... WHY? Why would you go to all that work for a motor that is basically obsolete? You already know that the valve seats are prone to fall out. All that fitting and machine work... why not just put a bigger cam in your 341, rebuild it and crank 18-20 HP out of it? Far less work, parts availability is better....
I mean, what's the gain? Overhead valves, that's about it as near as I can see.