FWIW, the 1x123 body works great with the Arc head if you use a single AA battery. I don't think 1xAA is enough to power the newer Arc heads, but it works fine with the Grey Kit, and it looks pretty sharp if you strip the HA off of the bezel.
I have also had my Arc LS on a Mclux pack.
If you can live with it being alittle longer than it needs to be, you can make a spacer to take up the needed space inside. If I recall, its about 1/4".
Heres a pic of a 2x123 Mclux Power Pack on a Arc LS, Arc Grey Kit, and the Mclux head.
****NOTE: There are NOT 2x123 batteries in the pack, there is one extended dummy cell. 2x123's will KILL and Arc LS.
But, this should give you an idea of how they look.
HERE are many more Mclux configurations that are possible.