No-one's actually specifically said in this thread that the GBH release is unsupported, and Keith has only mentioned working on support for the 1MB and compilation versions so far. I sent an email just in case - I'm sure his email box won't sustain any permanent damage!
I also investigated the DOS version of the original that Jeff presumably supplied and supported in his JST patch (which is the same as what he supported in his WHD patch IIRC, but only refers to Chris Vella's re-release in the readme). It doesn't work when you write the image in the WHD/JST archive back to disk and it's almost empty like the MFM version. Weird! I wonder where he sourced it from. I have a lot of Chris Vella's games on CD and James Pond isn't amongst them.