My son's boat (1986 50 hp Johnson) had its lower unit replaced. Now the forward and reverse are reversed. It runs fine except the shift lever conflicts with the upholstry and side wall of the boat, and can't get to full forward. (total running time under the problem is under ten minutes.) He's going to call the servicer ASAP, but I'm curious as to why and how, and could use the backup information as to causes when he talks to the guy who fixed it. Any ideas?