\documentclass[10pt,twoside,letterpaper]{book}
\usepackage[utf8]{inputenc}
\usepackage{amsmath}
\usepackage{amsfonts}
\usepackage{amssymb}
\usepackage{makeidx}
\usepackage{graphicx}
\usepackage{lmodern}
\usepackage{kpfonts}
% Let's set this as a half-letter sized sheet
% https://tex.stackexchange.com/questions/338789/how-to-set-paper-size-to-half-letter-5-5-x-8-5-in-in-amsbook
\usepackage{geometry}
\geometry{
	paperheight=8.5in,
	paperwidth=5.5in,
	heightrounded,
	margin=0.5in
}
% Adjust the top and bottom margins
% http://kb.mit.edu/confluence/pages/viewpage.action?pageId=3907057
\addtolength{\topmargin}{0.5in}
\addtolength{\textheight}{-1in}
% Set the header style
% https://www.overleaf.com/learn/latex/Headers_and_footers
\usepackage{fancyhdr}
\pagestyle{fancy}
 \fancyhf{}
 \fancyhead[LE,RO]{the codex}
 \fancyhead[RE,LO]{Issue \#001}
 \cfoot{Page \thepage}
\renewcommand{\footrulewidth}{1pt}

\usepackage{kantlipsum}

\author{Kenneth John Odle}

\begin{document}
\chapter{Introduction}
\kant
\kant
\end{document}