I've done a bit of digging about "Jack" & "Gwen". "Jack" was the original of this type whereas "Gwen" was a later development of what was the Hunslet "Waril" class but I can't find a full set of dimensions for the Waril type - oops just found them (Page 154 of "18 inch gauge Steam Railways"). There were originally 13 Warils, "Gwen" at John Knowles + 12 others at Deptford, four of these went to Sand Hutton being scrapped in the early 1930's one was also scrapped at Deptford about the same time and the last seven "probably scrapped" about 1938/9. I'll post the dimensions later today (when I have more time).
G
Gavin
Linslade
Bedfordshire
UK
Garratt Locomotives
[
www.beyergarrattlocos.co.uk]