create text blocks with zero pt leading

Here's a commented code achieving the goal.

\documentclass{article}
\usepackage{fontspec}
\setmainfont{Courier} % this is what I have
\usepackage[svgnames]{xcolor}

\begin{document}

\noindent\makebox[\textwidth][l]{% we don't want overfull box messages
 \renewcommand{\fontsubfuzz}{\maxdimen}% we don't want spurious messages
 \fontsize{42}{42}\selectfont % compute the text width
 \settowidth{\dimen2}{A}%
 \setlength{\dimen2}{16\dimen2}% 16 glyphs per line
 \parbox{\dimen2}{% start a \parbox
  \settoheight{\dimen0}{/}% measure the height of the tallest character
%  \addtolength{\dimen0}{1pt}% finer adjustment
  \fontsize{42}{\dimen0}\selectfont % set the baseline skip
  \lineskiplimit=-\maxdimen\lineskip=0pt % no lines are too near
  \parfillskip=0pt % paragraphs fill the line
  The \textcolor{DarkRed}{pitbull} lies\par
  well-behaved and\par
  chained /It belc\par
  hes and it snore\par
  s mutedly in its\par
  sleep /A melanch\par
  oly muzzle on it\par
  s snout.........\par
}}
\end{document}

Here is a possible solution. Not sure if it produces what you want. I edited a bit the settings so I can compile it without the required font.

You can adjust the vertical distance between baselines at the \vskip1.5ex

\documentclass{article}
\begin{document}
\thispagestyle{empty}
%\usepackage{fontspec}
%\setmainfont{Courier Std}
%\usepackage[svgnames]{xcolor}
\parindent0cm
\renewcommand{\baselinestretch}{0}
\def\crampled#1{\smash{#1}\par\vskip1.5ex}
 \fontsize{42}{56}\selectfont
\crampled{The {\color{red}pitbull} lies}
\crampled{well-behaved and}
\crampled{chained /It belc}
\crampled{hes and it snore}
\crampled{s mutedly in its}
\crampled{sleep /A melanch}
\crampled{oly muzzle on it}
\crampled{s snout.........}

\end{document}