Harmonizing plainchant for two voices

SuscipeMeDomine

Glory to Jesus Christ!

Are there any resources for harmonizing chant to be sung with two voices, with the original chant melody both above and below the harmony voice?

Below are some resources I've found that might be helpful. Any opinions on how they might be used?
Fux's Gradus ad Parnassum
http://www.newliturgicalmovement.org/2020/01/droning-at-mass-guest-article-by-mr.html#.YEQs7HVzS1E
https://orthodoxtwopartmusic.org/

Thank you!

Andrew_Malton

Perhaps this channel, although not right on target, would be of some interest: Chanter sur le livre à la Renaissance.

Jeffrey Quick

There are some examples here:
http://amiens.pwch.dk/Contents/Am162f030v.html
There are others, but you'd have to dig them out via RISM.
For things not necessarily note-against-note, and pre-done, see part2 of Morley's Plain and Easy Introduction, which is a fun read.
This is the edition I grew up with: https://www.amazon.com/Plain-Introduction-Practical-Norton-Library/dp/0393006824/ref=sr_1_2?dchild=1&keywords=Morley+plain+and+easy&qid=1615155735&s=books&sr=1-2
If you don't find facsimile, and have access to Early English Books Online, it's there, or probably elsewhere on the Net.