i have a dana 60 out of a 85 f250 a 10.25 out of an 87 250 laying around, my problem lies that i plan on using one of the to go under a welding trailer im making but i want to pick the strongest one. i looked up the 10.25 with an axle code of 39 and the weight rating is only 6250 where as my one ton dually truck has what appears to be the identical rearend with an axle code of 45 and its rated for 7400 pounds. What is the difference between the two, i need to have the heaviest axle i can get under the trailer since i think it will probably weight around 7500 pounds loaded!