The torque peak on my 55 235 (175 ft-lb) is at about 2100 RPM. With 205R75-15 tires, a 3.90 axle ratio and a 70% overdrive the 60 MPH cruise is 2076 RPM - right about the sweet spot. If you used big tires, like 255R70-15 the 60 mph cruise would be 1895. It might feel a little sluggish climbing from 40-60.
I have the 3sp manual with BW OD tailshaft in my truck, which also is a 70% overdrive like the 700R4. It has 390 rear axle and 205R75-15 tires. It works very well.
BTW, at the risk of starting a religious war, if you're changing the rear to open drive and changing the trans to a modern automatic, you're no longer "restoring" the truck. And I'm fine with that. My advice is, since you've already decided to modify the truck, don't let purism get in the way of building a truck that you'll enjoy owning, driving, and sharing with the public.
Leon
