The switch to large journal was in 1985.5. But as above if yours is small journal, it's just much cheaper and easier to add in an electric pump near the fuel tank.
The switch between external balance and internal balance was in 1987 or 1988, depending on what source you use.
Any block that doesn't have provision for a mechanical fuel pump will be large journal, since that change happened after the switch to large journal.
I'm not sure what the 3.4 has to do with the conversation, but if you were thinking you could swap 3.4 internals into a 2.8 block and have a 3.4, that won't work. The crank itself will swap into a large journal block, since the crank is shared with the 3.1 (3.31" stroke). But the bore of the 3.4 is larger.
The 2.8 and 3.1 share the same bore, 3.503"
The 2.8 stroke is 2.99"
The 3.1 and 3.4 stroke is 3.31"
The bore of the 3.4 is 3.62"
So you can swap a 3.1/3.4 crank into a 2.8 block, along with 3.1 pistons and have a 3.1, if you wanted. I did this many years ago, when I built my "Franken60" that also utilized FWD aluminum heads and intake.
Timing chains are interchangeable between small and large journal cranks. Rod journal sizing didn't change until the 3500 (LX9) was introduced in 2006. The large and small journal reference is to the main journal size.