Lonnie,
Compare this illustration to the analogous illustration in the 1954 Accessory Installation manual.
The 51 shows equal diameter hoses and fittings.
The 54 shows different diameter outlets on the deluxe heater and on the under-dash inlet fittings. It also refers to the bushings used on the driver's-side heater outlet and on the driver's side inlet adapter under the dash. I'll post images later today, if needed.
ADspudnut, what style heater do you have and what year is it? We can help you answer those questions if you can give us a good photo of the front of the heater box/unit.
