\setuppapersize[letter][letter]

\setuplayout[width=4.25in,
			 height=7in,
			 topspace=1.8cm,
			 header=0.72cm,
			 footer=0.72cm,
			 backspace=0.75in,
             location={middle,doublesided},
			 marking=on]
\setuppagenumbering[alternative=doublesided,
                    location={header,marginedge}]

\setuphead[chapter][header=empty]

\setupheadertexts%
[][section][chapter][]

\starttext

\chapter{This CHAPTER title is way too long: \nomarking{it extends way past the margin}}

\section{This SECTION title is way too long: \nomarking{it extends way past the margin}}

\dorecurse{7}{\input knuth \par}

\stoptext