I use a 123 block against the chuck to square the holder; I was saying that the thrust washer under my qctp top nut makes that be so accurate I haven't needed anything more. I'm sure using the tailstock would be the same. Six of one, half a dozen of the other.
The two pieces of drill rod are a type of center. When I already have a hole handy I've used a center finder to do the same thing. In both cases I'm feeling the offset. But I found that I was more accurate in practice with two pieces of drill rod. I haven't figured out exactly why.