8 1/4 rearend
easy to get parts for...one thing to watch out for is if its a 2.45 ratio you will need a different carrier to go to the gear ratios you want...I run 8 1/4" in my 75 340 duster, 400hp and no problems, but im not out torturing it either...if your draging id probably recommend going to an 8 3/4" or Dana