I answered part of your question on the other post for the same topic.
Here is a site that may help you tremendously. Look in chapter 4.
http://www.redbooks.ibm.com/SG245139/5139fm.htm
For most OSs, I believe I can say that 4mb is the default size for OS filesystems. To see your block size, you should be able to run a command on the volumes/slices. On HPUX it is something like "vgdisplay -v /dev/vg01/lvol". The information at the top will show it. Do a "man -k block" to find your command in your man pages.
You can set the blocksize when you create new filesystems. It can't be changed once you have created a volume/filesystem. You would have to backup the data and destroy and recreate the filesystem to change the block size.
You will have to create new filesystems to migrate data to or backup and recreate the ones you have.