Thanks Guys,
If anyone is interested in having a go, I have part-finished drawings and instructions – enough for someone determined to make their own, and I would greatly value comments and feedback. Let me know if you are interested.
There are several variants it could be made as Google for 'hudswell clarke" and add one of "Mary", "Carroll" or "Mighty Atom", "Southam" or "Southam 2".
For the record it weighs 23lbs, about 16" long is powered by a shower motor with a stall current of 7A and is powered by a 7Ah lead acid battery from a fire alarm. It pulled an 18 stone chap on a big driving trolley happily and after much slipping pulled me and another chap on the same trolley (just).
In terms of size , weight and performance it is about the equivalent of Tich.
Neil