Well looking in my T350 book, I think you may be right, the kickdown would ONLY affect full-throttle or near full-throttle shift points. We left our Ford c-6 kickdown unhooked for 30 years, didn't hurt a thing.
So you may be fine, but I'd hook it up and see where your full throttle shifts are. You can always back off early if you or the engine get scared.
They do shift out pretty low just lumbering thru the parking lot, but if you go say halfway down it should shift at 2500-3000. Full throttle shifts probably 4000-4500 since the carb is still kinda small.
