L3

I don't think there's any difference. I think what makes them a "special or plus" are the chaffer and sieve that come with them. Round or blunt tooth louvers?

there was also a "corn pac" version, been told they are all the same. they just came with a different package to better hadle corn (chaffers, ect.)

the corn soybean special was the main configuration difference over the straight grain machine. the corn plus took the corn soybean special package and added a few more options. the package cost less than adding all the options included in the Plus (or Pac) package individually.

That is my understanding anyways.