Do you have high-steer? Whose arms?
If it is stock, no high-steer, buy the rebuild kit from Marlin. It comes with everything you will need, including new, strong bearings.
If you have high-steer and the arms are not TG's get the 25mm bearing kit, if you have TG's high-steer they have to be machined for the trunion pins. TG's are .750 while most others are 1.0.