Earlier rev board:
Later rev board:
Can anyone explain this difference?
These are the data bus drivers/receivers. The earlier rev used 2 8T28s in a 16 pin package. Each chip supported 4 bits, requiring 2 chips for an 8 bit bus. The later revs, I believe that this started with the RFI version, used 1 8 bit DP8304 chip in a 20 pin package. Functionality is the essentially same, with the savings of one chip. This was most likely a cost cutting move, and nothing more.
I am proud to report that my working Apple ][ (1978 non-plus) has all three chips