The small carb, small cam and valve springs will be your problems. It won’t make any power with its tongue hanging out on the freeway. Mileage goes way down.
I have a friend did 3.91’s to a stock 1970 318. Was fine on local roads. Took them out pretty soon after driving it on the freeway.
I bought some 3.91’s and put them on a stock 273-2bbl driver car to see if they were in working order. 50 mph was the limit. Didn’t want to go on the freeway unless the foot was way down on the gas.
