I second the using the factory style setup to for sure protect the trans from a forgetful driver. It's very easy and cheap to do. Run your hot wire to one terminal on the govenor and from the other to the solenoid. This will let it drop out of od at just under 30 mph. If you can't find an under the footfeed kickdown switch you can use a starter switch mounted in a bracket to where the the accelerater linkage, arm, or fabricated lever will push it on in the wide open throttle position. It is wired with one wire to ground and the other to the distributer side of the coil. When you stomp the pedal it momentarily grounds the coil and this drops you into underdrive or "passing gear". Summary: one wire to govenor then on to solenoid, one wire from ground to starter button and on to coil, total cost under ten bucks and total time maybe one hour. One thing to remember is that this will always leave you in freewheeling so lock it out with the cable or have a good parking brake.
