Glenn,
I tried many years ago to run A Cheddar Puffin plant with an injector, and it was almost a total failure.
I say almost, because I did get it to work after a fashion, by taking the boiler very close to it's upper limits, and only then with no other steam being used, the engine was stationary.
I was using the smallest injector available, and there just wasn't enough pressure or volume from the boiler to get a continuous flow of topup water. It is still in a box somewhere, destined to be forgotten.
I suppose with one of the larger Stuart boilers, it might work, but I think you would be banging your head against a brick wall with the standard size of marine boilers.
John