203 FullTime - its a decent strong case and works good for its intended design, used from 1974 to 1979 and some 80,s / there are some Part-Time kits available and they aint cheap or easy to install / besides you would hafta drive a million miles to recoup the little gas money you save to pay for the expense of the kit / Interchange - the 203 has a weird figure eight bolt pattern and a different output spline count than any other t-case , so it does not swap out with any other t-case made , to change one out you either must also change the tranny or pull apart yours and change the output shaft and tail housing to run a 205-208 or 241 .also if you do change the 203 out you also haft worry about or change the full-time frontend , mainly because the newer t-cases are not designed to spin full-time. basically if you have a good running full-time truck leave it alone , grease the front wheel bearings and be happy