Most Dakota's had 3.55 gears so that's most likely the carrier for the lower gear ratio sets. If I remember right 8-1/4's also had an axle spline change somewhere along the way. Have you tried your axles to make sure they're compliant with the sure grip? Would suck to get it all set up and find out you need axles too. Are you using your old gears or installing new ones? I believe summit sells a pinion depth measuring tool specifically for the 8-1/4 made by Ratech