The subjects of this kit are the iconic broad gauge Rover 4-2-2’s of the Great Western Railway. They were replacements for the earlier ‘Iron Duke’ class and although known officially as rebuilds or renewals, they were essentially completely new containing very litle of the earlier engines. 
Unfortunately the twenty four engines which make up the Rover class exhibit many significant differences being built in four different sub-classes. The kit represents the 1880 built engines as that was the only GWR works drawing that was available during design. 
The six engines were all built at Swindon 
Bulkeley                  7/1880 
Dragon                   8/1800 
Great Britain            9/1800 
Emperor                  9/1880 
Sebastapol            10/1880 
Alma                     11/1880 
All survived until the end of the broad gauge on 20th May 1892. With a life of less than twelve years few changes to their appearance took place. Notably the whistles were moved from their original position on the firebox to the cab roof from c1890. 

The most significant change concerns the tenders. The Locomotives of the Great Western Railway states that the tenders originallly paired with these engines are variously described as of 3000 gallon or 3192 gallon capacity; these tenders will be described as 3000 gallon tenders. Photographs show the engines running with the earlier 2700 gallon tenders. These tenders had the same design of underframe, but with lower shorter tanks. From photographs dated from 6th July 1886, the pairings were: 
Bulkeley                 Always shown with a 3000 gallon tender 
Dragon                  Always shown with a 2700 gallon tender 
Great Britain           Both types of tender 
Emperor                 Both types of tender 
Sebastopol             Always shown with a 2700 gallon tender 
Alma                      Always shown with a 3000 gallon tender 
There is provision for both types of tender to be built. 

Sources of information and photographs are: 
Parts two and twelve of 'The Locomotives of the Great Western Railway' RCTS 
Broad Gauge Finale, Rev.A.H.Malan, Wild Swan 1985 
British Railway Journal – Special GWR Edition, Andrew Wiles, Wild Swan 1985 
G.W.Engines Vol 1, J.H.Russell, OPC 1975 
Great Western Broad Gauge Album, A.K.Steele, OPC 1972 
The Great Western Broad Gauge, Laurence Waters, Ian Allan 1999 
A Broad Gauge Album, Newton Abbot Museum & Broad Gauge Society 

The model is designed to Scaleseven Standards running on 49.2mm gauge track. 
Wheels. Because the prototype engine had such limited clearances between wheels, brake hangers and splashers the model is designed with slightly undersizes wheels. The specifications are: 
Driving wheel - 7’11” diameter, 26 spokes. Slaters’s ref S7895R 
Carrying wheels - 4’5”, 14 spokes, 5/32” axles Slater’s ref S7853RMF 
Tender wheel – 4’ 0” diameter, 12 or 13 spokes, 5/32” axles Slater’s Ref S7848RMF 
If you are turning you own wheels you should use these dimensions.