I think the 18" should be great, had one in my 46 for a while. That was with a saginaw 4 speed, had to modify the mount to the trans and shorten the rods to move it forward and clear the seat.
Since that trany I've stepped up to the S-10 T-5, comes with it's own shifter which is centered in the truck and with the old narrow 46 it made a huge improvement.
Best of luck
