Wanted: 1964 valiant rear differential

Hey all! First time poster. Cruising down the road In my '64 valiant, and a terrible sounding grind and clunk occurred. Upon close inspection, it appears my rear differential bit the dust. Anybody in or near Seattle have experience with a similar situation/where to get parts/have suggestions on what to do? Slant6, 225, push button auto, 4 door. I think it's all stock, and am guessing it's a 7.25", but I could be mistaken. Any ideas how to confirm?