Joe, this is not strictly about Ray Repp, but you may be interested in an album I bought several years ago which seems to fit the idea of his work: Rejoice! Music for the Worship of God in the Twentieth Century

I found several various books and albums confirming F.E.L. holds the copyright to the song, including:
- Sing praise! : sing praise to God with Ray Repp : [guitar and choir ed.] (this would be the ultimate source of sheet music)
- More children's liturgies by Bruck, Maria (which confirms your note above regarding Hymnal For Young Christians)
- Ray Repp - Come Alive
- Ray Repp - Sing Praise