In a custom documentclass, maintain chapter title headings but move page numbers to bottom

Question

I am using a custom documentclass provided by my school for writing my thesis, which is a modification of the documentclass book. They also give a template, which includes the line

\pagestyle{headings}

When this is activated, each page (that doesn't begin a chapter) has the chapter title across the top, and the page number at the top right. When the chapter title is long, it runs right into the page number, even overlapping it. When this is deactivated, I lose the entire heading, including the chapter title and page number.

I am aware of ways of overriding the documentclass file such as by specifying a different pagestyle (such as plain or fancy), but these also override my header.

I want to keep the chapter titles at the top of the page, but move the page number to the bottom. Do I need to edit the documentclass file, or is there a way to just redefine what "headings" does?

I know nothing about writing documentclass files but my guess is that I can get the desired effect by altering a portion of it that looks like this:

 \def\ps@headings{%
      \let\@oddfoot\@empty\let\@evenfoot\@empty
      \def\@evenhead{\thepage\hfil\slshape\leftmark}%
      \def\@oddhead{{\slshape\rightmark}\hfil\thepage}%
      \let\@mkboth\markboth
    \def\chaptermark##1{%
      \markboth {\MakeUppercase{%
        \ifnum \c@secnumdepth >\m@ne
          \if@mainmatter
            \@chapapp\ \thechapter. \ %
          \fi
        \fi
        ##1}}{}}%
    \def\sectionmark##1{%
      \markright {\MakeUppercase{%
        \ifnum \c@secnumdepth >\z@
          \thesection. \ %
        \fi

Answer 1

There are different ways. You can patch the original code to place the page number at the bottom. Or patch it to wrap longer chapter tites (example at the bottom). Other ways might be to remove the string CHAPTER or to remove all this uppercasing altogether.

All of those are changing the output of the template. Either way, using a package is better than patching low level commands:

\documentclass[11pt,a5paper]{book}
\usepackage{geometry}
\usepackage{blindtext}
\usepackage{scrlayer-scrpage}
\ohead{}
\cfoot{\pagemark}
\begin{document}
\chapter{Wombats are cute and cuddly, just like ducks}
\blindtext[3]
\end{document}

Wrapping the title:

\documentclass[11pt,a5paper]{book}
\usepackage{geometry}
\usepackage{blindtext}
\usepackage{etoolbox}
\tracingpatches
\makeatletter
\patchcmd{\@evenhead}{\leftmark}{\parbox[t]{.9\linewidth}{\leftmark}}{}{}
\makeatother
\begin{document}
\chapter{Wombats are cute and cuddly, just like ducks}
\blindtext[3]
\end{document}