LNER GRESLEY A1 CLASS LOCOMOTIVE KIT
A BRIEF HISTORY.
Just before Grouping, Nigel Gresley introduced his prototype 4-6-2 design on the GNR. There were only two engines of this class in service at the end of 1922, but a further ten had been ordered by the GNR and these were completed in 1923, the LNER. classification being A1. On Gresley's appointment as CME of the LNER this class was adopted as standard and a further forty (twenty by the North British Locomotive Company) were constructed in 1924-25. In 1927 two of the class were rebuilt with higher pressure boilers to become the first of class A3 and eventually, by 1948, all but the first engine were dealt with in this fashion. These engines were all built with the driving position on the right hand side. 

From this kit, which is for right hand drive engines, you can build these engines in their original condition as class A1 or after their conversion to class A3, until circa 1952-54, when they were eventually converted to left hand drive. 
For a detailed history of this long lived class Part 2A of Locomotives of the LNER published by the RCTS is essential reading. Other valuable sources of information and photographs are: 
The Book of the A3 Pacifics by Peter Coster. 
The Power of the A3s by Gavin Morrison.
Locomotives Illustrated 25 - Ian Allan 
The Gresley Pacifics - O.S.Nock - David & Charles 
Yeadon's Register of L.N.E.R. Locomotives - Volume One - Irwell Press 
East Coast Pacifics at work - P.N.Townend - Ian Allan 
The Power of the A1's, A2's and A3's - J.S.Whiteley & G.W.Morrison - Oxford Publishing Co.
Isinglass Drawings 327 and 328

VARIATIONS POSSIBLE WITH THE KIT.
Cabs.
The first eleven engines were built to the generous GNR loading gauge with high cabs. The remaining engines, except for 1481N, were built to the reduced, composite LNER loading gauge with lower cabs. The first eleven had their cabs altered to conform between 1928 and 1933. 

Cab sides. On the lower cabs the original cut-out was increased in height by 11" at the same time as bucket seats fitted. 

Chimney. Original high type for GNR loading gauge and lower type for the LNER composite loading gauge.
 
Dome. Original high type for GNR loading gauge and lower type for the LNER composite loading gauge plus the two types of banjo domes fitted to the A3 class with the later 94A boiler from 1940 onwards. 

Firebox. All the fireboxes fitted to A1 class boilers and to the first five A3 class conversions (Nos. 4480,2544/73/78/80) were similar in appearance with four washout plugs on the left hand side, & three on the right. With the next batch of boilers washout plugs were increased by one each side.

Firebox crown washout plugs/door covers. Originally square ended plugs and from circa 1936 onwards circular covers. 

Safety valves. Initially the locomotive was fitted with the large type for GNR loading gauge and later the smaller type for the LNER composite loading gauge.  

Frames. There were differing frame lightening hole arrangements. In their original condition these engines had four large oval holes together with a 12" circular hole ahead of the cylinders. However due to the surprising frequency with which frames were replaced or repaired the large holes either disappeared, were plated in from inside or were replaced by the 12" circular holes that were standard on the later new A3s.
 
Frame rivets. The original engines were built using countersunk rivets and so give a smooth appearance to the frames. Many photographs show a gradual change to rivets with a visible head as frames were repaired or replaced.  

Valve gear. All the engines were originally built with short travel valve gear with narrow platforms and steampipes which extended down to the level of the footplate. Between March 1927 and May 1931 they were rebuilt with long travel valve gear with wider platforms and shorter steampipes. This change alters the length of the crosshead arm and the arm below the radius link. 

Bogie. Originally the engines were built with the swing link bogies which were converted to the helical spring type circa 1933-34.
 
Bufferbeam. The first twelve engines had a rectangular bufferbeam. The corners were subsequently cut away to clear the platforms at Newcastle, as shown in the diagrams, later engines being built with this modification.
 
Front footsteps. Nos. 1472 - 81 were originally equipped with a light bar iron type. These were all removed by 1927. From 1935 onwards all the engines were fitted with a plate type and at the same time small grab handles were fitted to the front drop plate. 

Rear Steps. Nos. 1470 - 80 were built with a width of 8' 8" over the steps. The remainder were built with narrower steps with an overall width of 8' 4". 

Front end cover plates. Small cover fitted from 1933 onwards.
 
Rear spring retaining brackets. Fitted later. 

Anti-vacuum valve plate. Two types provided. 

Cab seats. Original type replaced with bucket seats from circa 1935 onwards.
 
Lamp irons - footplate. Second lamp iron on R.H.S. removed from 1931. 

Lamp iron - smoke box door. Two different types. 

Reversing rod. Different shape depending on whether Doncaster or North British built.