See https://github.com/AustralianAntarcticDivision/bowerbird
This script uses bowerbird to configure a new repository and populate it with all the R-devel tarball archives (you'll have to create ~/bower directory).
The configuration here unpacks each tarball at the end of synchronization checks.
The bb_sync(cf)
step can then be run on some routine schedule to keep the local repo up to date, allowing you
to forget about whether you have the latest emails and just trying whatever idea it is you had.