Doc, the problem with the 1940 is that the drive shaft and torque tube fit 1940 only because of the length.1937-39 interchange as do 1941-54...................The speed you want to cruise at will be determined on what you feel is safe for your engine.In my experiance I am comfortable with 3200 RPM for the engine long distance travel. Some fell this is too fast but has never given me or my traveling companians any problems..............With your present 4.11 your engine is turning approx.3066 rpm.at 60 mph..with a 3.73 it will be 2766 at 60 mph.and 3227 at 70.With a 3.55 it will be 2677 at 60 and 3122 at 70.(To the Power Glide owners your engine will be running a bit faster due to a slight torque converter slippage--The reason for lock-up converters on modern cars)(Packard aoutmatics had a lock-up converter in 1950 as well as Studebaker) ..............This is how Chevrolet described the difference in the 1937 Engineering Feature manual.........Greater economy,longer engine life and higher cruising and top speeds are attainable in the Master than in the Master DeLuxe because a 3.73 to 1 ratio is used. A sacrifice in acceleration and in hill climbing ,slight but noticeable,is,of course,the price to pay for the economy,life and speed that are gained.This was there economy line. I have found that 67-68 MPH on the speedo. is a comfortable speed for my 39,The only thing is the traffic Still is flying past.
