I looked up some possible options online and found BrakeBest Bleeder Screws. It said the 5/16"-24 screw, part# H9403-2, should fit the rear drum brakes and the 3/8"-24 screw, part# H9402-2, should fit the front disc brakes.
I went to O'Reillly's Auto and got confirmation on the part numbers and bought a pair of each type of screw. Got home, removed a rear bleeder screw and saw that they were NOT the 5/16"-24, but were instead the 3/8"-24 screw. I put the 3/8"-24 (which were purchased for the front discs) into the rear drums and they seem to fit well. Then bled the rear brakes and quit for the night. I'll be pulling the front bleeders in the next few days to see what size they are.