63' Nova/Chevy II rears are a drop out/3rd member type rear end. They "look" the same as 55'-64' full size Chevrolet cars, but are not; they have thinner cases, smaller bearings and caps, and won't hold up for long under any kind of power. However, the 55'-64' full size 3rd members will swap right in, and are a lot stronger, but the axles are still the weak point; they're small, but with an automatic, and being careful, should hold up for a while. The brakes are another story altogether! Been there, done that.