I did mine (2000 - 340) a few years back. I have some photos on this site of the job from engine and transmission, and at the throttle itself. Also the routing process.
From what I'm reading, the transmission being "stuck" in reverse....it may have been in reverse when it was attached on both throttle and transmission ends.
If the throttle itself is in reverse and the transmission also it may not go forward.
So my advice to you is double check the positions of the throttle on the engine and transmission before disconnecting either end. Label the new cables to not get them confused at the throttle.
But above all, be certain of "neutral" at all 3 ends (transmission, engine and throttle)
Aside from that, it's a fairly easy job, routing the cables being the hardest part.
Take your time, check and recheck as you go no points of the new cables kink. Make wide easy loops in the cable, but cinch them up tight to the existing bundle. To loose and they will cause throttle creep.
Hope this helped.
