One would hope that both top and bottom bearing cartridges were of the same fit family, if not the same diameter. But is it "safe" to assume so? Sure as the only risk is money. It the angles are not correct the you'll be back to a hard to adjust headset and only out a few $. But there's a way to measure first. The best way is to use a headset gage which measures diameters and angles of the seats and bearings. Most better shops have one. Andy.