I have rebuilt the Ultima V disk using all the valid data salvaged from the original disk. There are 11 non-recoverable blocks on the original disk and the corresponding blocks are filled with zeros on the reconstructed disk.
The missing blocks are evidently important, because the disk doesn't boot yet.
I don't own an Ultima V disk set myself, so the next step is to search the disk images I have found online for matching blocks to fill the gaps. Let us hope that the unrecoverable blocks do not contain your gamesaves data!