So after making the 6" to 3" reducer I decided to make the 3" 180deg bend. I took a trip to the scrappy and picked up some 3" pipe but had no luck with 3" 90deg elbows. Being impatient and having a limited window of opportunity to work on the column I decided to make the 180 deg bend out of the straight 3" pipe. The first time round the angles were a bit off and the two vertical pipes were nowhere near parallel so I had to pull it apart and do it again. The end result isn't perfect but it will do for now.
Being impatient I made the flange for the reducer before I actually received the tri clamps. I made the first flange from 1/4" tube then once the tri clamps arrived I found out that the overall diameter once flattened was too small. I then made the flange out of 3/8" tube but once again the diameter was too small. I ended up making the flange out of 1/2" and it is perfect.
I should also mention that I'm trying to make this entire column using soft solder only, just like all my columns.
I have to go past the scrappy regularly for work so I dropped in a week after finishing the 180 deg bend and look what I found :-D 2 90 deg 3" elbows. They are going into the shed and I'll remake the 180 deg bend later.