That's a good find, it looks neatly built.

I just use a block in such situations, but my trains aren't that long so maybe I'll be unpleasantly surprised when I start running longer trains.

I tend to use some thick rectangular or square styrene rod (Evergreen call theirs "strips").

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If anyone remembers, I have a penchant for ugly locos. 

An off-topic comment if ever there was one!

That looks like a nicely-built example of the K's kit; you're lucky to have it. You might want to consider renumbering. 2849 was one of a handful of 700 class engines rebuilt with the type D boiler in 1908/9, which did result in a degree of uglification:

[Embedded link to catalogue image of Midland Railway Study Centre item 82417, 2849 approaching Trent with a through goods train c. 1920.]

It went straight from this condition to a G6 Belpaire boiler in 1923, a type it retained until withdrawal in 1947:

[Embedded link to catalogue image of Midland Railway Study Centre item 99-0683, 2849 outside Derby No. 4 shed c. 1925.]

Tenders are a bit of a nightmare. By the 1920s, many 700 Class engines were running with either Johnson tenders off withdrawn 2-4-0s and the like, or with Kirtley tenders with rebuilt tanks, as in these photos of 2849.

An example of an engine with round-topped boiler and unrebuilt Kirtley tender, i.e. in the condition of the model, is 2834, renumbered 22834 in 1935 (2849 was renumbered 22834 around the same time). 2849 was a Derby engine for most of its life; 2834 was allocated at Leeds or Normanton up to 1930 but was at Birmingham in 1933, ending its days as part of Bournville shed's antique collection.

[Ref. S. Summerson, Midland Railway Locomotives Vol. 2 (Irwell Press, 2007).]

16 minutes ago, Miss Prism said:

Are those sandboxes hanging off the outside frame?

Yes, those are only a feature of engines rebuilt with D or E boilers, and retained when those boilers were exchanged for the G7 Belpaire boilers. The D and E boilers were second-hand off Johnson 4-4-0s that were being rebuilt with the larger H boiler and were a bit longer than the B boilers originally carried. The 700 class were built without any sanding gear but once steam standing had become standard (from the mid-1880s) they were fitted with sandboxes under the front framing, with sand pipes to the leading wheels. I suppose that these got in the way of the modifications needed to fit the D or E boiler, or possibly it was felt that with the increased power of the rebuilt engines, better sanding was needed. Johnson's earlier 0-6-0s were also built without sanding but the later engines had sand boxes from new, either side of the centre driving wheel; these were of the same pattern as those fitted to these 700 Class engines but being mounted on the inside frames and partly hidden by the footplate valence, were rather less prominent.

1 hour ago, AlfaZagato said:

I need to renumber my 812.   I plan to renumber it to be 'Donald' in about '32.

Ah, yes, I remember noticing that the twins carried the next two numbers after the real last class member, before they 'lost' them.