All you need to do is connect the MPCC to the Tring and insert that into the focuser, you dont need any extensions.
The MPCC, once screwed into the Tring should be at the optimum distance for the imaging chip, and actually my require 10mm of out focus.
Would be better if you did post pics, so we can see what you mean, though.
Focuser is too big?? Is it bigger in diameter than 2"? On a Skywatcher?