I have a job coming up that involves replacing a 4" lead closet bend
into a cast iron waste stack. For some reason unknown to me the lead
bend is rotting away at about 10 and 2 o'clock... maybe between 10 and
2. I couldn't see without a mirror and I didn't want to feel around up
there. The pipes are exposed in a stand up basement area, so have that
going for me.

My plan so far is to pop the toilet, hack out the old bend, install a
new 4" cast iron bend, pack with oakum and schmear in some plastic lead
substitute. The plastic looks thick enough to stand in the vertical face
of the Y.

Does this sound reasonable?

I was hoping to find a no hub clamp, but the guy at the parts place said
I would have to cut off the hub and that ain't gonna happen. I don't
think there would be anything left of the Y to clamp onto after the hub
was cut off. The hub is approximately 6" in diameter OD and the 4" bend
is about 4 3/8" OD. Is there a clamp that would connect these two? Or
does the first idea sound better?