Sorry, what I meant was the coupler slides over the raw end of the pipe about an inch. The Fernco I saw at the store, and it was an actual Fernco brand coupler, looked like these: http://www.fernco.com/plumbing/shiel...-hub-couplings
It had that rib in the middle that keeps the two pipes from touching, but they come pretty close.
Anyway, I'm considering the original Idea of cutting at the horizontal except about two inches from the vertical stack. The reason: the drain looks like it may have sagged over time and is sloped ever so slightly the wrong way so that the elbow is the lowest point.
I've heard ther are ways to attach the PVC right into the cast iron joint after drilling out the lead seal. Is this what they're talking about?: http://www.fernco.com/plumbing/donuts-o-rings/donuts
They general idea sounds promising but that in particular looks a little sketchy to me. Plus it looks like it reduces the size of the pipe to 3" and that doesn"t seem desireable to me.