Is it a 79 K20, or is it a 89K2500, or a 99K2500HD?
If it's a 79 K20; You will have a 14bolt gm corporate full floater rear and you will probably have a gm 10 bolt front.
If it's a 89 K2500; You will have a 14bolt gm corporate semi floater rear with IFS.
If it's a 99K2500HD; You will have a 14bolt gm corporate full floater rear with IFS.
As far as your differential carrier in the IFS applications; I don't know which is which.
Respectfully,
Dave