The standard 3-speed truck tranny in '54 was a Muncie. There was also an optional heavy duty 3-speed by Warner Gear. If you can find the serial number stamped on the flat spot on the left side of the case just to the rear of the side cover, you can verify which tranny it is. The serial number will start with M for Muncie, or W for Warner. I'm not sure either of these went by any particular name or model number.
BTW, welcome to the 'Bolt, BiG_MaN! You will find this place to be very informative--usually.
