Looking at the Haynes current flow diagrams for 1974. Am I correct in assuming the small numbers on the wire tracks are the wire gauge in millimeters?

Seems right...

0.5 mm = 0.020 in ~ AWG 24
0.75 mm = 0.030 in ~ AWG 20
1.0 mm = 0.039 in ~ AWG 18
1.5 mm = 0.059 in ~ AWG 14
2.5 mm = 0.098 in ~ AWG 10

From memory I belive they are mm^2 numbers, but the translations to AWG look correct.