Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
Rear axles are different - 2500 has a 14 bolt semi-float and the 3500 has a 14 bolt full float, in most cases. Also, appears you could get a 305 in the 2500 but not in the 3500 (obviously a LD 2500).
Full float was optional in a 2500, I believe a diesel or big block automatically got you one.