Thank you Joshua. I am processing this quickly so I may be mistaken, but what I see is :
1 - The introduction is by Dunster's SON, and contains nothing of interest, but typical clerical affirmation that the soul has an eternal existence.
2 - The text itself is wholly clerical and contains nothing of interest. To the extent it refers to the ancients, it doesn't mention any Epicurean views - just circular representations of god and the like.
So what we are missing, which might have been of interest if it still existed, was Dunster's OWN commentary on the issue of eternity. Looks doubtful we will find anything based on this.