Hi Mike,
Perhaps we should start a 'mystery loco' section!

I did a bit of searching when the loco first came up for sale but
couldn't pin it down to any known design. It's obviously designed for
very tight radius curves due to the centre wheel flanges having been
removed. I would think it probably is a freelance design. The tender
resembles some fitted to Baldwin locos. Perhaps you could post some
better photos when you get the loco?

Zoe is a 2-8-2 narrow gauge loco for gauge 1 but is more like a 3 1/2"
gauge loco in proportions. It appeared in Model Engineer vols 116 and
117.

Little Jack Horner is a gauge 1 2-6-2 narrow gauge loco which appeared
in vols 65 and 66. There is a photo in 'LBSC'-His Life and Locomotives
(essential reading!). Your loco does bear some resemblance to LJH in
that both have connecting rods driving the rear axle.

Your loco appears to be virtually complete so I wouldn't worry too
much about its origins. Just get it running and enjoy!