The 1948-1955st Truck Shop Manuals have the same instructions as posted by zoegrant (after a u-joint cover has been opened and gear-oil drained) "Remove speedometer gear and fill housing with transmission lubricant." (in Chapter 4)

The same manuals have the following instructions in Chapter 0, General Lubrication (1/2 ton trucks):
- Universal joint . . . receives lubrication from the transmission. Additional lubrications is not necessary.
- This type of lubrication is on 1/2 ton vehicles.
- The universal joint housing should be filled through the pipe plug hole for initial lubrication after a repair operation.


go figure - either way should work - watch for drips (fill as deemed necessary - either way/level )