Confused on casting number and suffix code

[Deadman walking]

So I ran the number on the front pad of the engine under the passenger side cylinder head. it came back to a 1980 C-20 square body truck block K1030TDF. but then I run the casting number behind the cylinder head on the driver's side 10054727. it comes back as an 86 only block I'm just confused on this which one? Unless its a 80-86 block.