Rear Axle & Bearings

[ltown]

I have a 78 F100 and my rear wheel bearings on the driver side have gone bad and i need to replace them. All of the auto parts stores i have called or gone to have asked me the axle weight and type. I have the weight but im having problems determining the axle type. apparently it could be a ford axle or a spicer... how can i tell the difference or is there a label somewhere that can answer my question?