Thanks, Irish, the second link had just what I need. D'akujem pekne.
I studied Slovak 20 years ago for family reasons and the rules seem to be close except for the placement of the accent - not indicated in Slavonic and regular in Slovak - and the length of vowels - indicated in Slovak by a mark on the vowel.
Of course one would expect the pronunciation of Slavonic in a Ruthenian church to follow the rules for Rusyn when written in the Latin alphabet. But finding that information is no easier than finding a direct answer to my question.