I still have a couple cases of Old Milwaukee returnables here - the glass is a lot thicker and more durable. I think your best option is to do a soak in Oxyclean, although that would certainly remove your labels. You could just fill them most of the way with water, then dose each bottle with Oxyclean to loosen the crud. Then hit them with a bottle blaster and follow up with a bottle brush. If the case was closed, chances are that there's not too much junk in there. However, I doubt the bottles were rinsed before storing, so they could have some extreme crusty mold going on. Good luck!