The 426 probably doesn't have needle bearings for the piston pin - they usually just float in the piston / rod end and get fed pressurized oil from the crank..
It sounds like it got hot / ran low on oil and seized the pin in the rod. What's weird is that the piston doesn't move on the pin. That's bad. Before replacing the rod, check the price of crankshaft kits: on some bikes a new crank/rod kits with bearings and seals costs less than repairing what you have.