Ah rats, 2 things he's done I forgot to mention, compression check and carb synch.
Then I'd look into a fuel delivery problem; perhaps right where the T branches out to left & right banks. Really lean running carbs can cause high cylinder temps.
I'd try pulling the spark plug caps one at a time while the engine is at idle; the cylinders doing all the work once pulled will cause the engine to stumble badly as the lazy cylinders will not affect the idle much when the caps are pulled.