I'll try to answer the questions more or less in order.
1. I will have another shooter try it out this week.
2. The front sight appears centered on top.
3. I'm right handed. I have a Model 66 that shoots very accurately for me.
4. Distance was about 15 feet. 125gr 38 hand loads and 158gr American Eagle Magnum loads. Same issue.
5. Tried both the factory grips and the VZ 320s. Same issue.
6. I'll see if the range has a bench I can borrow.

It could be entirely my issue but at 15 feet in single action I was off 4-5 inches.

I shoot my K frame just fine. I'm no sharp shooter but I can generally put everything inside the big circle without trying.

My results were also from shooting outdoors. I'll try indoors and have a a friend shoot it as well.