All I can do is refer you to the introduction by Trevor Giffiths to his teleplay for THE LAST PLACE ON EARTH, (his take on SCOTT OF THE ANTARCTIC) as well as the book POWERPLAYS by Mike Poole which deals with it. So far, I've not read any in-depth discussion of the changes and have two books about Griffith on order by inter-library loans, the most recent by John Tulloch published by Manchester University Press.
Trevor Griffiths is very busy at the moment working on a stage adaptation of his screenplay about Tom Paine, THESE ARE THE TIMES, which Richard Attenborough was to film in the 90s but now seems very far from any film version. Griffiths mentioned how busy he was to me when I emailed him about an article I was writing about David Mercer.
From what I've inferred from the references I've read to the changes, the original screenplay became a victim of Reagan's election at the time, something that also had much to do with the adverse reaction to Michael Cimino's HEAVEN'S GATE.
Griffiths has a Web site but I don't think there is much information there and, at this moment, assuming he would agree to an interview, would only do it at a pre-arranged time in London.