Thank you Thomas.
I'm now happily using XTerm 347 on Gentoo using the attached ebuild file
in a portage overlay.
It's a glorified copy of an earlier ebuild, renamed for the new 347 version.
--
Grant. . . .
unix || die
# Copyright 1999-2019 Gentoo Authors
# Distributed under the terms of the
Files:
ftp://ftp.invisible-island.net/xterm/current/xterm-347.tgz
ftp://ftp.invisible-island.net/xterm/current/xterm-347.tgz.asc
ftp://ftp.invisible-island.net/xterm/patches/xterm-347.patch.gz
ftp://ftp.invisible-island.net/xterm/patches/xterm-347.patch.gz.asc