If you mean fork tubes, they're all 35mm, plus the the offsets and fork spacings remain the same. Here's a pic of a 73 CB500 with an idea of spacing for the gauge bracket bolts.
Using an online fische all the CB500's plus the first couple year CB550's (74-75) are the same I thought there were differences in the boss width for guage bracket bolts, but apparently there were tha same for several years??