Through a GLAM collaboration with the British Library, some rare old Bangla language books were obtained which were written in Sylheti Nagari script. One such example is this book, see one page of it.
With regard to this, for our readers, it is necessary to be able to unilaterally convert this Sylheti Nagari script to Bangla script, which is the script of choice for Bangla language. Bangla to Sylheti Nagari script conversion is not necessary.
Here is the community discussion for this proposal.
Here is one existing transliteration tool for the scripts with source code in this repository .