Actually there might be, I was going to op for the edelbrock microswitch/relay set up, but after parts and labor kinda expensive........
I got to looking at things and think I found an easy and cheap solution, some GM cars have the turbo 400 kick down switch mounted in the cabin working right off the gas pedal, gave me an idea...... On the 67 you have a square nylon pad in line with the gas pedal rod that goes to the pedal itself, it is the stop for the pedal rod itself when you floor it and that part of the gas pedal rod that hits the stop is flat which is great, the pad pops right out of the firewall and the hole for it is inline with gas pedal rod that goes to the pedal, I ordered a weather proof heavy duty push button switch that looks like this.......
http://www.ebay.com/itm/Heavy-Duty-R...b4b589&vxp=mtr
I will open the hole up for the switch and use the switch as a pedal stop, some large flat washers, install, then adjust depth with proper size washers so when you floor it it will activate switch.....
Then hook up wires from old switch, cover it nicely the part that protrudes in the engine compartment in 3m strip caulk since it is in a pretty harsh enviroment and the strip caulk will make it weatherproof and done...... For less then $10.00 in parts you have a heavy duty 16 amp kick down switch with no brackets, no relays and simple.....
Also the way my customer drives I think the little rubber weather proof boot will last a long time as he dont punch it often........
If you dont want to drill holes in your truck, the Edelbrock microswitch set up is the way to go, but if you dont mind enlarging an existing hole in the firewall then the push button set up...up to you

For me, it all comes down to money the customer wants to spend.... $100.00 parts and labor for it to downshift is pricey in his eyes which I can understand since I am doing so much other stuff to the truck for him which aint cheap.......
Will tell you how it works out.....