I have a 67 swb with factory over drive tranny. Where do I find parts such as the solenoid switch, governor and kick down switch?

Seems the stock rear axle ratio for a truck with this tranny is 4:11. Has any one changed it to a 3:73 or 3:42 and if so how did it work out? Most of the driving will be on the highway but I will also use it to creap around on the farm. It has a stock 283 ci. engine with RV cam.