any regular cab 73-79 d44 or 78-79 bronco d44 will work. the most desireable are the 78-79 d44s. these axles have reverse cut high pinion diffs. cast on radius arm tabs, and disk brakes. the reverse cut gears are supposed to be a little stronger than standard cut, but they are also high pinion, with means that the driveshaft attaches higher up than the ones older than 78. this is important when lifting a truck so you driveshaft angle isnt too bad and doesnt bind up. on your 89 you have to lift 6" for the axle to fit under it and not bang against things when your out bouncin around. you will need the entire axle hub to hub, the radius arms (the 80-96 ones are tottally different and will not work), the radius arm mounts (they are bolted to a crossmember on the old style it would be best to take the entire crossmember) and the coil buckets, because the old syle springs that attach to the new straight axle wont fit in the 89 spring bucket (the ttb springs are also too stiff for a straight axle the rates are different). you need all the steering linkage and the trac bar and its mount. also grab the shock mounts or get them off an 80s f250. these older radius arms use bushings to correct for lift. the bigggest bushing you can use is 7deg offest and that is only good for 4" of lift. you will have to drop the radius arm mounts at least 2" to do the swap. some just run 4" drop brackets from any aftermarket company for the ttb or the 70s style. it may actually be easier to use the 4" drop ttb brackets. the hardest part for most is the tracbar bracket. your 89 was never meant to have one so there really isnt a place for one. a place called cage offroad should have one out now when i talked to them it was gonna go for $110. just do some reasearch on the internet theres lots of guys with pages just about the swap. have fun with it good luck!