There are a few that make this style, but by far the best and most common in Baker Monitor. What you have is a Baker Monitor standard pitless unit....it's unually used on heavier installations than residential. The 1.25" is where you thread the pull pipe, and gravity is the only think that is holding the unit in place (the industrial units have a hold down spider and set screws, but you would have mentioned that....check out baker monior web site). The upper casing diameter should be 7" for a 6" well (or 1 pipe size larger than th actual well casing), and the pitless unit you have drawn the top of is sort of like a spool from a hydyaulic valve that mates with a housing when it is seated. There are two o-rings on top and under where the water exits. If this was installed anything out of perfect vertical alignment, they can be difficult to install and remove. They can be hard to pull if they have been in place for a long time, by that, meaning you just have to pull hard. There are no special tricks, just pull straight. You may want to order a new set of o rings before you start this job. If this unit is on your well, it probably means you have a deep set pump, and/or heavy pump, probably steel drop pipe....you won't be able to do it by hand, and you will need a crane. This unit is expensive and a little labor intensive to install, so I doubt they would have done that for a small pump on poly. Good Luck.