You may not have the Merril MCK or SMCK, but what you have may be similar.
Picture is from
https://terrylove.com/forums/index.php?threads/another-pitless-adapter-question.41692/page-2 and is not a Merril MCK pitless. But the the mechanism is similar. If you shine a bright light down the middle of that 1 inch pipe in the middle, do you see a shape similar to that picture? It will be down around the frost line. Some people have smashed a pipe to make a tool to fit over that shape and turned that CCW fully. That would retract the arm that presses the big o-ring toward the casing where the hole in the side of the casing is. There is also a tool made for the purpose, and Merrill has the ones for their pitless units.
Now on your picture, note there seems to be a saw mark at the 5:30 position. That might mark the spot over the hole in the casing. If so, that means you have rotated the crossarm. I suggest that you replace the big O-ring when you put things back together. Use silicone grease on the new o-ring. The pitless has to fit over the hole to pass the water. It is up to the installer to do marking, and you will need to be careful to get things alligned during installation. After you get your extended casing welded in place, you will need to replace the current pipe that connects the cross bar to the pitless with a longer one. It is the length of that pipe that gets the alignment vertically.
My well casing top and the pitless cross arm are shown in the attached photo.
The reason we used this type of pitless is that it allows a 3.75 inch pump to fit into a 4 inch steel casing. If I went to the common Merrill B10X trapezoid type, it would have either required a 3 inch pump, or would have had to have excavation of the pit floor to fit an adapter assembly, or the pitless would have ended up a bit above the frost line (which might have been OK). But the SMCK, even though it cost more, did the job letting my existing pump that had been in service since 2002 go back down the hole.
Do you have a 4 inch casing?
