I am pretty sure Mack is the only one who uses the pumpkin with the rear cover facing down. I guess that's their preference.
Others use "regular" positined axles and have a shaft coming out of the forward axle to drive the rear.
tandem axle trucks use a single speed rear axle and the transmission has a split output to give it more gears.
some have a split input too to give it a super low reduction and a double overdrive.