Zappatime,
I built an Ace models kit of the ex LBSCR K class on 7mm and in spite of all of the members of my club warning me not to buy one, I did, and it went together very well and ran even better, I put a HOG motor in it and it would manage 13 coaches around the club test track.
I believe that Bill Ascough himself once described his kits as an aid to scratchbuilding, regardless of that I found the K enjoyable to build.
If there is a down side to this particular kit it was the lack of instructions for it, if I remember rightly there were about three pages of A4, sparsely illustrated, an access to pictures of your chosen prototype is certainly a must.
Pete