A E N Z O K O M O W N A M
let’s write down the ordinal numbers of letters in the alphabet
1 5 14 26 15 11 15 13 15 23 14 1 13
subtract each value from 26
25 20 12 0 11 15 11 13 11 3 12 25 13
write down the letters corresponding to the ordinal numbers (0-space)
Y U L (space) K O K M K C L Y M
MYKKY MULLOCK?
other options are possible
This is could be easily debunked by asking you why you’ve chosen those specific letters for the non-Latin glyphs.
This is could be easily debunked by asking you why you’ve chosen those specific letters for the non-Latin glyphs.
You are right, the choice of these non-Latin glyphs is not accidental. It was they who suggested which method exactly to decrypt this message.
The cipher code is not long enough to make full use of frequency analysis. As previously presented by a respected glurk, the number of suggested options will be too large to select the only correct one from them. I think that the person who made up the encryption Z408 and Z340 understood this perfectly.
I assumed that he might have hidden clues on how this cryptogram could be deciphered. At first I started looking for clues in the body of the letter itself, but did not find anything suitable.
Then I focused on the encrypted message itself and found that he was using new glyphs here, not the same as in previous messages.
This one
And this one three times
Why use the new glyphs? Maybe they contain the secret of solving this cipher?
I would ask a rather strange question, but did Zodiac use the whole English alphabet in Z408 and/or Z340?
Mullock means "rubbish" or nonsense".
The assumption that this glyph means the letters K in O. Or in other words, K turns into O, and O into K. This is possible only if the letter orders are subtracted from 26. This is a hint how to decrypt this cipher.
In turn, the glyph 
probably means Z, and this one is obviously W.
I think Mullock is not a real name, rather a nickname. Maybe he’s Italian
