The 1390131 model has the square aluminum badge that many people prefer. (the 1390120 has it too, but lacks the LED panel so it is less desirable)
Somewhere about early 1989 they changed from stabilizer wires on the larger keys to the plastic insert sleeves (the spacebar kept its wire, of course) and sometime around then, or earlier, they made the metal plate lighter. The earliest plates were shiny and yellowish, later they were dull and gray.
In the early 1990s, the plates got even lighter. I like old stuff, but it really doesn't make much difference. I would suggest that a novice buy a new Unicomp with the USB plug and get into vintage stuff on a hobby basis.
You could also buy a 1390120 for cheap and swap its plate into a newer chassis when doing a bolt mod.
I have never convinced myself that stabilizer wires are better than the barrel inserts, either.