What could cause this? 360 problems ####update####

Another confusion, when I installed a new timing set in my 273, I was surprised that the dots on the sprockets lined up (closest together) when #6 cyl was at TDC. I thought someone was wrong, but before creatively "fixing it", as I sometimes did as a dumb kid, I checked the Shop Manual and found that is correct. My timing set had the 3 sets of marks. I set for 4 deg advanced, to give slightly better low-end torque and mileage, plus that accounts for future timing chain wear.