[Tex/LaTex] Change the default headers of the book class

Question

I am writing a thesis and my university requirements are to use 14pt fontsize for the body text with 1.5 line spacing. They require the chapter headings and the word CHAPTER #N to be in ALL CAPS, however the running header should be in Title Format. Here is a picture of what I need:

So far, I was able to accomplish the following:

Now I need the running headers to be in Title Format as given by first picture. The following is the code I wrote to center the chapter headings and change the default running headers of the book class. But I was unsuccessful in getting the running headers as in the first picture.

\documentclass[a4paper,oneside,14pt]{extbook}
\usepackage{newtxtext}
\usepackage{setspace}
\usepackage[top=25mm,bottom=25mm,right=25mm,left=30mm]{geometry}
\usepackage{lipsum}
\renewcommand{\chaptername}{CHAPTER}
\renewcommand{\contentsname}{TABLE OF CONTENTS}

\usepackage{fancyhdr}
\pagestyle{fancy}
\fancyhf{}
\addtolength{\headheight}{0pt}
\lhead{\itshape  \chaptername ~\thechapter}
\rhead{\itshape  \leftmark}
\renewcommand{\chaptermark}[1]{\markboth{#1}{}} % remove "Chapter N." prefix
\cfoot{\thepage}

%% Center Chapter Headings in both front and main matter.
\makeatletter
\def\@makechapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \centering\normalfont
    \ifnum \c@secnumdepth >\m@ne
      \if@mainmatter
         \huge\bfseries \@chapapp\space \thechapter
        \par\nobreak
        \vskip 20\p@
      \fi
    \fi
    \interlinepenalty\@M
     \huge \bfseries #1\par\nobreak
    \vskip 40\p@
  }}
\def\@makeschapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \centering
    \normalfont
    \interlinepenalty\@M
    \huge \bfseries  #1\par\nobreak
    \vskip 40\p@
  }}
\makeatother


\begin{document}
\begin{titlepage}
\centering
Some Info here.
\end{titlepage}
\frontmatter
\chapter{DEDICATION}
\chapter{ACKNOWLEDGMENTS}
\chapter{ABSTRACT}
\tableofcontents
\chapter{LIST OF ABBREVIATIONS}
\chapter{LIST OF FIGURES}
\chapter{LIST OF TABLES}

\mainmatter
\onehalfspacing
\chapter{INTRODUCTION}
\section{First Section}
\lipsum[2-16]

\chapter{RECOMMENDATIONS AND FUTURE WORK}

\singlespacing
\begin{thebibliography}{100}
\end{thebibliography}
\end{document} 

I appreciate your suggestions.

Answer 1

textcase is your friend here. I would not hardcode the uppercasing in the titles itself for several reasons. The main reason is that uppercasing them makes it impossible to have no uppercased titles in the header - what you try to achieve. Unfortunately you can't use titlsec because you need to uppercase in the redefinition of the chapter-head (when you don't hardcode the uppercasing in the titles itself!). Here is the code:

\documentclass[a4paper,oneside,14pt]{extbook}
\usepackage{newtxtext}
\usepackage{setspace}
\usepackage[top=25mm,bottom=25mm,right=25mm,left=30mm]{geometry}
%\usepackage{titlesec}
%  \titleformat{\chapter}[display]{\centering\normalfont\huge\bfseries}
%    {\MakeUppercase{\chaptertitlename}\ \thechapter}{20pt}{\huge}
\usepackage{fancyhdr}
  \pagestyle{fancy}
  \fancyhf{}
%  \addtolength{\headheight}{0pt}% obsolete
  \lhead{\itshape  \chaptername~\thechapter}
  \rhead{\itshape  \nouppercase{\leftmark}} %\nouppercase !
  \renewcommand{\chaptermark}[1]{\markboth{#1}{}}
  \cfoot{\thepage}

\usepackage{textcase}

\makeatletter
\def\@makechapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \centering\normalfont
    \ifnum \c@secnumdepth >\m@ne
      \if@mainmatter
         \huge\bfseries \MakeTextUppercase{\@chapapp}\space \thechapter
        \par\nobreak
        \vskip 20\p@
      \fi
    \fi
    \interlinepenalty\@M
     \huge \bfseries \MakeTextUppercase{#1}\par\nobreak
    \vskip 40\p@
  }}
\def\@makeschapterhead#1{%
  \vspace*{50\p@}%
  {\parindent \z@ \centering
    \normalfont
    \interlinepenalty\@M
    \huge \bfseries  \MakeTextUppercase{#1}\par\nobreak
    \vskip 40\p@
  }}
\makeatother

%\renewcommand{\chaptername}{CHAPTER}
%\renewcommand{\contentsname}{TABLE OF CONTENTS}

\usepackage{lipsum}

\begin{document}
\frontmatter

\chapter{Dedication}

\tableofcontents

\chapter{List of Abbreviations}

\mainmatter
  \onehalfspacing
\chapter{Introduction}
\section{First Section}
\lipsum[2-16]

%\singlespacing
%\begin{thebibliography}{100}
%\end{thebibliography}
\end{document}

Note that I included the titlesec attempt as uncommented code lines.