You are right Alan, the Hornby 
Deltic chassis is far too long for 
the A class body, hence the the 
chassis has to be cut in the middle 
and Deltic fuel tank removed. 
When you buy the A class resin body, 
you get the fuel tank sides and a bit of 
plastic card will finish off the missing bit 
in the middle.The resin kit also comes 
with the bogie side frames which match 
up nicely on the Deltic bogies. 
My workbench has some photos 
of my build of a39.