When i first saw your research i was convinced you had solved it! After learning more i don't think you have.
TB would have wanted Robert Morriss to decode the ciphers, locate the treasure and pass it on to the rightful heirs. That means to me, that all 3 KEYs would have the same book cipher format and the decoded text would be in the same dialect/style as the DOI.
I understand the the use of old English as added protection but to make the ciphers uncrackable all TB needed to do is randomly assign letters to numbers and use multiple numbers for the same letter. There is no need for two layers of encryption and then use old English.
Based on my research ive concluded the 22 alphabetical string at location 480 provides the needed protection but still maintains the KEY format of the DOI substitution cipher.
To demonstrate this method i used the 22 letter alphabetical string to redact, four miles from bufords.
I have deposited in the county of Bedford ABCDEFGHIIJKLMMNOHPP, in an excavation or
vault, six feet below the surface of the ground, the following articles, belonging jointly to the
parties whose names are given in number three herewith:
Now, if TB used the 22 letters to redact "five miles east to a rock", i contend you will never decode this action/instruction because these three variables; distance, direction and marker provide too many combinations/alternatives to narrow it down to the correct location.
There are three other shorter strings that could easily be used to redact any two of the three as well as single letters sprinkled around.