240 to 208 is a 32V drop, so the 1000VA suggests a current rating of 1000/32 = 31A. But the link says 24V. So the 1000VA should be about 40A.
If that is a suitable current for your loads, with a margin of 25% to 50% over the actual draw, then the VA is acceptable.
How are you planning to connect this transformer?
Since you have just one high line, connecting one transformer in "semi-wye" from the generated leg to input neutral (not the same as 3 phase neutral, which you do not have), and taking the tap to your output would be correct.
That, assuming the transformer is OK with the 15% high voltage, should give you 248V on the output. That's still a little high, but not bad. Since the actual winding as connected will be for 240+24= 264V, the 276 is not much over that. I'd not expect an issue.
Typical connection is to connect H2 and H3, X2 and X3, and finally, connect H1 to X4
Then connect H4 to "input neutral", X1 to the RPC generated leg output, and take the actual output from the H1/X4 connection.
Having the transformer connected may foul up the start, So I suggest that some means be used to not connect it until the idler has started (switch, contactor, etc).