David,
I've also got an original riveted saddle tank, which I'm pretty sure is a Davenport. It is rusted out at the steam dome hole, so M-C probably replaced one of their tanks with a new one. The only way to tell for sure if it's Davenport, would be to look for the "D-", which proceeded the casting number, on the water filler casting. McAnally used a prefix of "M" for their casting numbers. While the 10x16 and the 11x16 Davenports look basically the same, the 10x16s used smaller eccentrics, while the 11x16s used the same eccentrics as the 12" cylinder locomotives.
Dave