\setuppagenumbering[alternative=doublesided, location={footer,right},page=no]
\newdimen\Margin
\Margin=2cm
\newdimen\MarginRaise
\MarginRaise=56ex
\setuptexttexts[margin][][\setups{text a}][\setups{text b}][]
\setuptext[leftstyle=\sc,rightstyle=\em]
\startsetups[text a]
\raise\MarginRaise\hbox{\vtop{\hsize=\Margin%
\startalignment[right]
\getmarking[chapter]
\stopalignment
}}
\stopsetups
\startsetups[text b]
\raise\MarginRaise\hbox{\vtop{\hsize=\Margin%
\startalignment[left]
\getmarking[section]
\stopalignment
}}
\stopsetups
\starttext
\chapter{First}
\section{first}
\dorecurse{6}{\input tufte}
\input tufte
\input tufte
\input tufte
\input tufte
\chapter{Second}
\section{second}
\dorecurse{6}{\input tufte}
\chapter{Third}
\section{third}
\dorecurse{6}{\input tufte}
\stoptext