You can wire the overdrive trans up not needing engagement cable or foot switch. My installation in 63 C10 went like this:
Used side plate (4-bolt) and shift arms off original three speed. This allowed the use of stock shift linkage arms.
Wired with toggle cut off / cut on switch for solenoid. Now when I want overdrive, flip the switch to on, accelerate to about 30MPH, let off gas and she shifts into OD.
There is a thread with lots of information and pictures. I tried to copy thread below but not sure I did it right but you can search on "3 Speed Overdrive" and the post you want is "3 Speed Overdrive, Now about getting it it"
http://67-72chevytrucks.com/vboard/s...d.php?t=313886