Classic/Antique Car Repair: 1948 willys pickup truck, rear axle ratio, cubic inch engine

Question
I am getting this truck running and trying to find out the speed range of the current transmission Borg warner T90. I would like to replace with a tranny that would get me to 70 mph on the freeway?

Answer
It is not the transmission that will give you what you want, it is the differential rear axle ratio. There was however an overdrive unit that was offered for these trucks when new but the small 226 cubic inch engine is a but sluggish to wind the this truck up to those speeds.