This is the joint you see at the midsection of the telescoping plunger arm.
Measurements based on NDP Plans.
I added a tube at the bottom to push into the larger portion of the plunger arm to help secure it and have something to glue to.
The OSD of addon tubing is 27mm.
The ISD overall is 18mm to give 1mm of clearance on the 17mm OSD telescoping tube.
Print orientation: I would suggest printing this with the tapered section down with a build plate.
Density: My suggestion on this is 100% mainly to give strength to the section where it gets glued on.
If you need an alternative sizing version PM @bryanxiii