Bigger aint always better
Ill repeat the question, why bother? The 351C head with the stock valve flows about as good as it gets anyway. Having raced with Clevelands and knowing, over the years, several other people that have done the same, The stock valve size in the 2 bbl cleveland head will flow all you can ever get into the cylinder, up to and over 8500 RPM. The gain by going to a larger valve just isnt worth the effort. You are better off getting stainless one piece valves of stock size and go with that. The only people I know of that ever opted for larger valves were the guys running the 4 bbl head, and they are considereably larger valves anyway.
The stock valves in the 2 bbl head are 2.04/1.65 and the Limas ran a 2.08 inch intake with the same sized exhaust valve.
4 bbl cleveland heads had a 2.19/1.71 valve combination. If you are set on going to larger valves, go with the 4 bbl head jobs. But then the final question is, what are you going to do with this engine? If its a going to be a street engine, stay with the stock valve size, and concentrate on cleaning up the valve bowls and the exhaust runner. You will get a lot more out of it that way then just putting in bigger valves.