Very interesting drawing. Some differences from the Horwich 18" locos, the first two of which were delivered on 7th April 1887 - (Dot and Robin - BP 2823/4) at £250 each.
A third was delivered on 8th November 1887 for £300 (Wren - BP 2825) and the remaining five were built at Horwich (with a price hike like that I'm not surprised!) - Wasp and Fly in 1891, Mouse and Midget in 1899, finally Bee in 1901.
The last three were built with well and saddle tanks, the others having saddles added later.
Dimensions that might be of interest:
Boiler 2ft 3in x 5ft 2in with cylindrical firebox 17in diam; 55tubes 1.375in od; grate 1ft long, area 1.78 sq ft; hs tubes 40.64 sq ft, firebox 7.22 sq ft; wp 170psi;
Cylinders 5 x 6in; wheels 1ft 4.25in diam; wb 2ft 9in.
Frame length 7ft 4.25in, total width 3ft; ht to top of chimney 7ft 4.5in, to boiler centre 2ft 9.5i.
Well tank 26.5 galls, saddle 50 galls weight empty 2t 19cwt 2qr and working order 3t 11cwt 2qr
(From Transport and Railroad Gazette Sep. 1904).
Allen link motion was used. Gear change was by lever on the LHS of the boiler unlike the Parnell loco which was on the RHS and appears to be screw.
Dot, along with Fly and Bee were withdrawn in 1930. Wren, now in the NRM, was the last to be withdrawn in 1961.
May your wheels never rust.