The shifter on my '47 had the same symptoms (from the day my older brother first bought it). The 4.022 housing (see Don's picture above) was replaced along with the interlock, cover and the shift lever (the pin had huge "slop" through the ball). The shifter motion improved immensely. IMHO the NOS housing helped more than the interlock, but on any given truck, the wear could be worse on either.
Have fun,
Bill
