Hyatt bearings were pretty popular 30-something years ago when I was running a truck shop. Do you have a readable number from the bearing you have removed? The cone (with the rollers) and the cup that it rides in will have different numbers, and both must be replaced to get a good result. The cup is usually a press fit in the hub, and needs to be driven out with a hammer and a soft steel drift (not a chisel or a hardened punch). Most bearing numbers can be cross-referenced to another brand by a good parts man. Try to get a good oil seal number while you're at it.
Jerry

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