There actually was an article on someone who did a fair bit on the underframe on the old RMweb, which I did on my model - sorry cant remember the name. If memory is correct, theres alot of pipework missing on the Hornby model, and the engines are too small and wrong. the Bachmann 150 lends itself here handily as alot can be transplanted off of that onto the Hornby model including the Gangways which Hornby messed up also
Edit:
I remember getting rid of the Hornby body and coverting a Dapol 155 as the share was much better, I have the remains of a Hurst models kit about to put up on the well known auction site. I think ive got a few images around somewhere also back when I was trying to improve my models when I had them
NL