You can see the changes in iw_15.iwd in maps/mp/gametypes. The old files are in iw_07.iwd. It shouldn't be that difficult to make it work with 1.3.
Like in _hud_playerscore.gsc they changed updatePlayerScoreHUD() to updatePlayerHUD().
Also if the mod in 1.0 already had a _teams.gsc you should the menu cvar loading part from the _teams.gsc from 1.3 into your gsc. Otherwise your default team menu from 1.3 won't show any team.