The 680 is a "forward" manual. The other is a "reverse" manual. The forward shift like a stock patern. The reverse, 1st is where 3rd would be and 3rd is where 1st, would be. Depends on the shifter you have, which one would be best for you. The reverse is used to prevent you from shifting into nuet. or reverse, by mistake, if you do not have a ratchet type shifter. I have a forward, as my B&M shifter is a ratchet. In other words, I can't shift into reverse without pulling up on the ratchet lever.
You would need a "shift kit" to make the tranny shift harder and faster. The manual valve bodies make you shift manually,with more possitive shifts. You will have no kick-down (passing gear)