Dear Shelagh,
I presume your MS was related in some way to NE Scotland. Just possibly, some details about the forces required could help, like was there an instrumental line?
RC chapels in the NE were acquiring organs at this time. Preshome St Gregory`s (south of Buckie) put up their Bruce organ in 1820 and a related letter that year said the choir was improving greatly. Tynet Chapel (Fochabers) installed a Bruce organ in 1824; Inverness Chapel likewise in 1837, and St Peter`s, Buckie, got an organ in 1840.
I have also checked on the Scottish Catholic Archives using the RISM search engine, just in case you hadn`t. There are 516 pieces listed, but no Happy Mary.
From the absence of replies to your query, I reckon there are negligible numbers here with similar research interests!!
Several of us are struggling to find the origin of a small church organ, of c. 1830 and probably Bruce, which could have come from an Episcopalian or RC chapel in the NE, and this brings home that definite facts on C19 church music for the countryside here are meagre. This organ is now nicely restored in Monnickendam, Amsterdam, and the Dutch call it "Het Schoste Koororgel". We know it came from Forglen House, Turriff, to All Saints, Aberdeen, in the 1930s, and went thence to Holland in the 1980s, but how did it reach Forglen.