4.88 was a common ratio for the 50's because most states still had a 45 mph speed limit for trucks. Although the engines are rated at 2100 most pumps were set at 2300 which allowed close to 60 mph. 4.33 and 4.11 were the fast ratios of the 60's. Is the 2 speed in high or low. If its in low, high would probably be around 4.11 which is as fast as your 671 will break the wind anyway. Are you talking about the truck you posted on May 23? If so, the picture with the cab hanging from an A frame clearly shows S cam brakes. Spring brakes will bolt right on to where the single chambers were. Did someone tell you that they were wedge brakes or are we talking about 2 different trucks. You will of course have to plumb for the spring brakes, but that's no big deal. I'm not so sure that the wedge brakes were available until the mid 60's and were short lived in popularity. Truck frames have been 34" for over 60 years and almost any rear end will fit. However, 2 speeds became obsolete in the 70's when hp ratings and torque ratings almost doubled.
