I recently picked up a CD with This Song of Love & listened to a short cut of Happy on the Way at CD now.

Both of these sound like 7 shape Gospel songs. Even though Happy on the Way says fa sol la singers, it is not in The Sacred Harp.

The first pass through the music is singing the notes. If you can hear people singing re's and do's you know you have 7 shape. I don't know a good source for this stuff in print, much less online. Conventions like the Middle Georgia one recorded would put out a new book every year that contained a mix of favorites along with new songs. The number of these books published prior to 1940's is almost unlimited.

If you want to take a look at 4 shape music see Southern Harmony.