Well I decided to do a little more looking into the lower units on my engines. The early 25SS engine I have has the classic deep skeg lower unit. This engine has the square exhaust opening in the tower housing. The later 25SS has the short skeg with the single water inlet hole and an exhaust snout that is round. My early 25XS has the exact same tower housing and foot while the late mode 25XS has the very short tower and the lost foam foot. I guess the lost foam unit is a result of the tooling to make the classic die cast items to be either worn out or scrapped in a cleanup. I can take some photos if anyone would like.