The data on the motor's website spec is: "Full Load Current - 6.2A at 230V, or 3.6A at 400V" ...close...
Anyway you can't judge much by these figures. They are strongly dependent upon the motor acting like a motor - no longer the case.
I've never made the calculations work very well at predicting performance myself (goodness knows I have tried).
IMHO using calculations to show that your motor, when converted, will do what you expect is a stretch.
Even more difficult to forecast is the efficiency of the machine when you're done. If you can get that 300 Watts with 50% efficiency, then you're doing well.
Kind of why I'd rather steer you toward an axial-flux generator, but it's been pointed out to me once already that it's not my project to decide.
On the other hand, you will have many electrical options if you choose that motor or something like it. It will also be pretty rugged and be easier to mate with the turbine your partner eventually comes up with. Why don't you take a look at my project and see what happens when giving one of these motor-conversions a load test:
www.sparweb.ca The "Baldor" conversion is the most detailed, but there's similar info on the "Toshiba" conversion which was a much larger 7.5HP motor to begin with.