I have a latex 260 that has doubled sided printing and I can tell you...at least on my machine, it blows. It is not practical at all and takes forever to reload it accurately and even then I never had any luck getting it within about 1/2" of registration.
try loading the material, advance it to an easily repeatable spot on the platen, print the image in the center of the roll, unload the material, flip the roll around, place the lead edge in the same spot as before, print the image again in the center of the roll (except flipped around).