Revised my snapshot script to build a .dmg to go with the source .tar.gz:
#! /bin/bash
# Make a snapshot of an XCode project's contents, excluding the large but reconstructible
# files in its build subdirectory, and save it as a compressed, timestamped archive.
appname=${1%/}
archtime=`/bin/date +"%Y-%m%d-%H%M"`
/usr/bin/tar zcf "$appname-$archtime.tar.gz" --exclude "$appname/build" "$appname"
# Make a distributable disk image of the application bundle.
if [ "$2" != "" ] ; then
tempdir=$appname-$archtime
/bin/mkdir "$tempdir"
/bin/mv "$appname/build/$appname.app" "$tempdir"
/usr/bin/hdiutil create -srcfolder "$tempdir" "$tempdir.dmg"
/bin/mv "$tempdir/$appname.app" "$appname/build"
/bin/rm -r "$tempdir"
fi