(First time poster just catching up on the news. Well done to all involved.)
Just thinking about period 19, now that we know the plaintext and key.
This is the 1960s, simple times so probably worked by hand with paper and pencil.
Write down the plaintext onto 3×5 index cards, they have around 9 ruled lines for writing text.
Which means the resulting message would be 19 columns wide.
Write the text in columns from top to bottom, one character per line on the card.
IRO HET OHS PAO EVF YIF ONA UGN ALI
Etc. for 19 columns
Then, encode the plaintext characters to cyphertext. This explains the period 19 bigrams.
Finally, read across the rows instead of down the columns, when transcribing the cyphertext from card 1 to the final work sheet.
Block 2 is the second index card. Same procedure.
Final two lines are grafted on the bottom. He can’t encode them vertically so just does substitution and reversal only.
To be consistent with his previous message, he writes the result as 17 characters per line to the final output page.
This could also explains the ‘pre positioned’ text for “LIFEIS” if he wrote that on the index card first, and then skipped those character places when transcribing the index cards to the output sheet.
Is it really that easy?
Hello, welcome Mr Youshac 
Well, I guess so, it’s easy (I’m not an expert)
Imagine a disturbed, lonely citizen with free weekends (it seems obvious that Z didn’t have a girlfriend)
The guy writes a text, codifies it.
Then he transcribes the way he wants on another page of grid paper and numbered with the distribution sequence he wants.
I Say for exemple , symbol 7 first square, 8 tenth square and …etc
There, it’s done.
It is what I think.
Marcelo 
https://zodiacode1933.blogspot.com/
You can see the required paper size here:http://zodiackillerciphers.com/images/z340-and-z408-on-grids.jpg
Not that this size of paper is necessary, but I had it available at that time
https://zodiacode1933.blogspot.com/
Is it really that easy?
I believe you are using a 1-dimensional period while in the Z340 it is a 2-dimensional period.
OK, thanks for the followup.
I still think that the reason Z used 9×17 blocks is because they fit neatly onto 3×5 index cards.
Such index cards would be very familiar to any clerical worker in the 60’s.
[a college librarian, for example…]
