Yeah there is lots of info there, just takes alot of time finding stuff of interest. Its surprising though what you can find if you take the time.
This particular A6M5 Zero is the only one still flying with the original Sakae 21 engine (1695 CID). The others are all flying with some variant of the P&W R-1830. I don't see how a slight engine change would affect the roll rate that much.
Please ask him what he thinks the maximum roll rate is on the A6M5 he flies, and "Does he know that he is contradicting NACA Report 868?"