I shall indeed make a list :o thanks. This is what I got so far XD I hope youtube is a reliable source for which songs are which.
Pallet Town -> Pallet Town
Viridian Forest -> Viridian Forest
Cherrygrove/Mahogany (The same?) -> Viridian City
New Bark Town -> Pewter City
Azalea/Blackthorn City -> Cerulean City
Violet City/Olivine City -> Lavender Town
Celadon City -> Celadon City
Cianwood City -> Fuschia City
Routes 38 and 39 -> Route Theme 1
Routes 3-9 and 22 -> Route Theme 2 Oak? -> Route Theme 3
ark Cave/Ice Cave/Seafom Islands -> Route Theme 4
Lighthouse -> Saffron City
Routes 42-44, Lake of Rage -> Mt Ember
Pokemon Center -> Pokemon Center
Hall of Fame -> Hall of Fame
Since FireRed's song table has half the songs that Emerald does, you'd have about half a megabyte of wasted space from Johto's songs. The most efficient way would be to assemble the S files manually (because I have all the ROM-ready S files) instead of c/p'ing the song data from Emerald to FireRed.
Would you mind making a list of what songs from HG/SS you want in your hack, and what vanilla songs you want to replace?