Pitman Arm

Hi All.
I recently bought a new pitman arm for my '74 Challenger, unfortunately it doesn't fit. The splined shaft diameter is larger than the one on the steering box so it's way loose. I converted my car to manual steering many years ago. Not sure if the manual steering pitman arms have a smaller spline or I have an earlier model ('70 '71) steering box on the car.
Anyone know whats the deal?
TIA

Early manual boxes used a smaller diameter output shaft than the power boxes.

All E bodies with manual steering came with the smaller spline size, they sent you the wrong part. The larger size was OEM on '73-4 cars with power steering.

Thanks Guys for clearing that up. Order was my bad, I just assumed it was a '74 steering box.