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.