How could I use the memoir
package (or anything else, that's just what came to mind) to output a letter paper size document, but typeset with a different page width (9" by 7" in my case) with a trim mark showing where the letter paper should be cut?
I got this far with memoir:
% !TEX TS-program = lualatex
\documentclass[showtrims]{memoir}
\usepackage{lipsum}
\settypeblocksize{6.5in}{*}{.75}
\trimFrame
\settrimmedsize{9in}{7in}{*}
\settrims{0in}{0in}
\begin{document}
\section{First section}
\lipsum
\end{document}
This shows the trim marks where I need them, but the typesetting is clearly still based on the 8.5" by 11" letter page. Is there any way to make it typeset on the 7" by 9" page?