Chevy offered an OD for cars and trucks from 55 through 69. The later OD transmissions (66-69) were full syncro. You should be able to find one at most swap meets, craigs list or ebay. If you have a 55-61 truck it is a bolt in, if you have a 62 or later with the short tailshaft it will require a driveshaft modification.
I use a GM cruise control switch for a kick down switch. They are available at Napa or most parts stores for about $10.
Fred
