No it won't work , first thing of many differences is the spline inside the ring gear which connects to the axle is larger on the 300 than on the 250 -------- I talked with one of the guys that is involved with getting after market ring and pinions for the 250/350 rear differentials into production and he says there is a hold up , so there is no after market available at the moment , I doubt you will find a good ring and pinion , look for a whole differential