going to a super six set up won't affect anything in the vein of "preservation of the car". it's all on the motor. BUT you will have to upgrade to a throttle cable and not throttle rod if the car hasn't been done so already.
as RRR said, if you can't find or don't want to pay the $$$ for the brackets/kick down you'll need to have jr high metal shop fab skills, some creativity and a little bit of understanding of how the components work together.
of course you could go with an aftermarket cable bracket/kick down set up, but it will 100% look modern in an otherwise vintage engine bay.
anyway, i'd back the truck up. read and research first before you go upgrading willy-nilly.
also, i'd recommend fixing the starting issue first. that would be a good project to get your feet wet on.