Dennis, use your parts catalog, go to text section 30, page 6 in the front axle parts list applications...see what parts lists are shown there for 1979 F350 4WD's.
Now go to the parts lists themselves.

30.5AA is in section 30.5, page 24, the other three are in section 30.5, page 12.

Read down the columns....whadda you see for basic part number 1A055 under those appropriate parts lists?

I see nothing!

Post this illustration: Section 30 / page 17..1976/79 F250 4WD & 1979 F350 4WD = the entire front axle assembly is shown.