hi tm, your 68 + 69 dart 383 4 speeds use a 7290 joint, 51.53" , 3" dia part # 2852 212 shaft. how about a stock dodge b body 383-440 8.75 shaft. same 7290 u-joint ,52.07" long , and 3" diam . part # 2852 162. I know I have extra lengths kicking around just for this reason. do you have 51.5" between center to center on your joints? ronnie