In the beginning the Avodah (service) of Karbonos was with the bechor (first-born -- see the mishnah in the last perek of Zevachim. The avodah was done by the bechorim until the Mishkan was built) until after they made the egel ha'zahav. Then the Avodah was given to the Kohanim and Shevet Levi. They (Kohanim) received matnas kahunah (chozeh, shuk, etc) because of their service in the Mishkan (and Beis Hamikdash.)
Before the egel ha'zahav to whom would these presents be given to? The bechorim?