Okay, I DID IT! Thank you "theducks"
TXT -> MOBI
I used the following settings:
Look & Feel -> Extra CSS: p{font-family:monospace;}
Structure Detection -> Detect chapters (XPath expression): blank
Structure Detection -> Insert page breaks before (XPath expression): blank
TXT Input -> Paragraph style: off
TXT Input -> Formatting style: plain
TXT Input -> Preserve spaces
And it worked
The output looks like the original text file.
A lot of trial and error but it was very useful for learning what Calibre can do.
Thank You!