Driveshafts are different, replace the swinger bearings. Not a tough job. If the end of the driveshaft that goes into the diff is rusty and grooved, you'll be moving into the rebuild of the rear diff. A clean driveshaft will only be ruined going into that old pinion seal. Not to hard but requires some special tools that can be made. Look at "The curious case of Jim's SX" thread.
1985 Honda 125M (My first Trike--Still have it)
1986 Honda 250SX
1981 Honda 110
1982 Honda 110
1986 Yamaha YFM80 (Sons quad)
Past rides: 1983, 1984 200X, 3--1985 Kawasaki T-3
1987 CR-80, 70's vintage XR75, RM 370