The Vigenere Cipher chapter is getting pushed back, but I'll do it soon, I promise. Here I have a decoded Caesar cipher.

This is the whole two pages. Now here's a closeup of the code:

Using the three letters back variation of the Caesar Cipher, this becomes "90% sure he's a werewolf." This is funny because it references Soos in the very first episode of Gravity Falls. Soos also believes the mailman to be a werewolf.

And they may be right. That guy has been around for a while. Assuming he is a young adult at the time Ford is cataloging everything in his journal, he may be immortal. He looks relatively young when we see him in S1E1. But that's just a theory! Let me know what you guys think in the comments.