I picked up a 1981 JD 1840 row crop (same as 2440) last fall and was curious about the speeds. JD made this tractor in 8/4 and 16/8 speeds and if you look at the tractor it has 8/4 speeds per shift levers, but it also has the Hi-Lo selector. Is this how JD makes a 16/8, as the Hi-Lo selector...