Penev, who named nine overseas-based players, included Luzern's Rangelov for the first time since a friendly appearance against Ukraine last November while Las Palmas's Delev last played in a friendly against Kazakhstan in June.
Penev, 46, who dropped strikers Valeri Bojinov and Iliyan Mitsanski, will complete his squad with home-based players after this weekend's round of the domestic championship.
Bulgaria, who have failed to reach the World Cup finals since 1998, visit leaders Italy in Palermo on September 6 and then take on Malta in Ta' Qali four days later.
Unbeaten Bulgaria are second in Group B on 10 points from six matches, four points behind Italy. Czech Republic are third on nine points, followed by Armenia and Denmark on six. Malta are bottom on three points.
(Reporting by Angel Krasimirov; Editing by John O'Brien)
