6v - 12v bulb chart from Tim Lederman's site.
Not sure about US made bulbs. Might try an internet search using the bulb number.
This is the original 6v bulbs and converted 12v bulbs in my '54 gauge cluster:
One bulb in the ignition switch housing:
6v = #51: 1 candle power, 1.7w @ 7.5v
12v = #53: 0.7 candle power, 1.7w @ 14.4v
Two bulbs in gauge cluster:
6v = #55: 2 candle power, 2.9w @ 7v
12v = #57: 2 candle power, 3.4w @ 14v
Two bulbs on each side of speedo:
6v = #55: 2 candle power, 2.9w @ 7v
12v = #57: 2 candle power, 3.4w @ 14v
Two indicator bulbs in speedo. Both bulbs are surrounded by 1/2" ID cardboard tubes with colored plastic lenses. Red for high beam, green for turn signal.
Top lamp is for high beam indicator
6v = #51: 1 candle power, 1.7w @ 7.5v
12v = #53: 0.7 candle power, 1.7w @ 14.4v
Bottom lamp is indicator for factory installed turn signals. '54 was the first year with an indicator lamp for turn signals.
6v = #51: 1 candle power, 1.7w @ 7.5v
12v = #53: 0.7 candle power, 1.7w @ 14.4v
Later model 12v trucks used a #57
