\documentclass[letterpaper,10pt,oneside]{book}
\usepackage[T1]{fontenc}
%\usepackage[defaultmono]{droidmono}
\usepackage[scaled]{beramono}
\usepackage{fancyvrb}
\usepackage{geometry}
\usepackage{pdflscape}
%\usepackage{showframe}				% Diagnostic

% Suppress headers and footers completely
\pagestyle{empty}

% 66 lines per page, portrait
%\geometry{top=0.0in, bottom=0.0in, left=1.0in, right=0.5in}
\geometry{top=0.0in, bottom=0.0in, left=0.5in, right=0.5in}

\RecustomVerbatimCommand{\VerbatimInput}{VerbatimInput}%
{
	commandchars=\\\{\}
}

\begin{document}

% Part 1 (main document sections)
\VerbatimInput{part1.txt}

% 51 lines per page, landscape
%\newgeometry{top=1.0in, bottom=0.5in, left=0.0in, right=0.0in}
\newgeometry{top=0.5in, bottom=0.5in, left=0.0in, right=0.0in}
\begin{landscape}

% Part 2 (appendices A-G, source listings)
\VerbatimInput{part2.txt}

% back to standard geometry
\end{landscape}
\restoregeometry

% Part 3 (appendices H-I, index)
\VerbatimInput{part3.txt}

\end{document}