How difficult is it to replace the knuckle thy the brake caliper mounts to? Previous owner stripped it and I'd prefer to replace it. Do
I have to remove the axles and open up the rear end?

 

all you have to do is remove the caliper, hub assembly and axle shaft.
then remove the nuts on the ball joints that hold the knuckle in place.
then hit the knuckle with a bfh till it falls down/off.
replace with new knuckle, and install above in reverse order.

pay attention to factory torque spec's.

watch yer toes when the knuckle falls off.