From The RadioReference Wiki
19A703241G1-G8 DELTA/S UHF/VHF MICRO 19A703868G1-G5 & G7 DELTA/SX UHF/VHF MICRO 19A703244G20-G23 DELTA/SX UHF/VHF and RANGR VHF MICRO 19A703868G6 Special for RANGR UHF only 19C851149G1-G4 DELTA/S Low Band MICRO 19C851149G5-G12 DELTA/SX Low Band MICRO 19C851591G1 DELTA/S Low Band MICRO (SOLDER IN FIELD KIT) 19C851591G2-G3 DELTA/SX Low Band MICRO (SOLDER IN FIELD KIT)
Look on the inside of the radio with the control cable connector pointing towards you. The micro is the large IC in almost the center of the radio. To the left of the micro is another 16 pin IC. Just to the left of that IC you should see the board number.