O S Nock got a good hard footplate run on a Duchess from Crewe to Carlisle very late in their career; it's described in the June 1964 Railway Magazine. It beat the Class 40 timings.
Regarding single Class 20s, I guess this was no problem as long as steam locos were about - long nose forward they still provided a better view. Once steam was gone however someone seems to have decided it was unsafe. I wonder why. US diesels long had the cab at about the 3/4 position, and most were driven "short nose forward". However a couple of their major railways, like the Southern, ran them the other way round, cab controls turned round, as "long nose forward", just like a steam loco. Apparently done to give the crew greater protection in any level crossing accident. That opposite view seems to have been done for safety, as well.