Found these pictures on AutoZone site , is this the steering coupler your after?
Housing and the repair kit listed separately.
Used to replace these by the dozens , till Dodge quit using them , on the replacements , we would drill and tap the housing and install a grease fitting to force the water out , they weren't particularly water proof.
Looked the part up for a 79 W150, the splines onto the steering box might be different , but it looks like someone is still producing them.
99DSDP 3884, Freightliner, XC, CAT 3126B, 300 HP /ALLISON 3060
2000 Caravan toad, Remco & Blue Ox.