Well, what do you have to work with for pedal and firewall bracket and linkage? Anything? Do you have a pedal with a bell crank that goes thru the firewall? We don't want to start suggestion things until we know what's there already. What are we adapting to, if anything? Pics would be very helpful. If you don't use a cable on the pedal, all the way to carb, you use a bell crank. From bell crank it's either a cable or rod linkage to the carb. I can't see the proximity of components to suggest a method. I always feel good about 100% linkage. No cable.
Where does this idea/comment come from? "I am not too keen on drilling more holes through the firewall to install a mid 60's gas pedal and linkage."
The 60-66 linkage covers it's own hole anyway.
