I recently located an unpublished translation, made probably in the 1850’s, of this work. This is now online here. The translation is public domain so copy freely and put online elsewhere, etc. I hope to get the Syriac online if I ever get 5 minutes to spare!
I have some doubts that this is really by Marutha. The text contains almost nothing about the deliberations, and everything in it could be sourced from Eusebius. The extra details all feel like fictional embellishments, and there are many anachronisms in it.
The manuscript has slumbered in Yale University for 150 years. The notes on it by AHW are by Austen H. Wright of the American Mission at Urmia in the 1850’s. He was one of the missionaries who set up a press there and printed the Syriac Peshitta Old Testament in 1851.