Yes, descibing fan belt noise. Here are the two different pulley sizes ( from a generator) . Sorry, just saw a 1940 truck, I understand . On the picture of both, the 5/8 is on right 3/8 on left. Let me know if this helps. The 3/8 (smaller one) comes almost to a "V" point at bottom. The 5/8 does not if you can see that in the pictures.
