Hiram,
You can make some quick and effective barrel blocks by casting them from linotype alloy. Just make up a shallow box tray from scrap lumber and notch barrel supports at each end. Pour in molten linotype until it reaches a little less than half barrel thickness. Repeat for the other half.
Another way to make blocks is to use hardwood (hickory, maple, oak, etc) and gouge out a barrel channel to match the chamber area of the barrel. Mke the blocks full vise jaw width.
I use talcum powder by itself or combined with rosin to coat the barrel before tightening onto the blocks. Don't be shy about how tight you squeeze that vise. You won't hurt it! It's usually easier to use a mallet or piece of 2"x4" wood to rap on the wrench to loosen the barrel and then tighten it back up until the sights index correctly. If too tight, repeated tightening and loosening will bring it into alignment. If too loose, you may have to make up some shim washers.
