Here is a link to an extremely rare book titled, AO Ken Temeshi (Sacred Hymns) in AO Naga. Published by the American Baptist Mission, Impur, Naga Hills, Assam 1900.
The PDF of the full book can be downloaded for free here:
This book is copyright free and public access material. Please feel free to download and freely distribute.
Here are a few page examples of this incredibly preserved book.