Just to round this off, I got the tube and some rings and I can get focus with the QHY5, the DSI2 and the QHY8, as it is. The starlight with the wheel could not. This is a 10" GSO dob with a cheap as R&P focuser. I think the lock screw is plastic
I measured 10mm spare infocus when the QHY8 was plugged in and it's sensor is 22mm from the coupling so another 10 is needed for DSLR focus.
I'm guessing the moonlight focuser I ordered will solve these issues and I won't need to trim the tube.