I think HopCar has answered your question about flow rate, and the pump does seems to be fairly water-resistant. I take the point about the Bakelite pump casing though.
If you want to consider an alternative, I used a March DC-4C-MD pump on my 31k btu system. Aprox double the horsepower of the CalMarine, but still a fairly small pump at around 10" x 4". It is not submersible, but neither is my generator, and they sit side by side. The body is stongly made of polypropylene (looks like nylon to me) and the impeller is magnetically driven, so no seals to leak. I bought three from eBay a couple of years ago for around $80 each: one for the a/c, one for the water-maker, and a spare for the next project.
If all else fails, read the instructions
If it ain't broke, don't fix it