As was obvious on the test image I attached earlier in this thread, my combination has a problem with working distance.
This was partly because of very confusing and non-standardised terminology used by amateurs and equipment suppliers, partly because I was using adapter combination similar (or same) to
this one.
The required (maybe?) working distance for Meade series 4000 0.63x focal reducer is ~61mm (for Canon camera), and the one I have has ~68mm total length.
I could not find the variable adapter neither low profile T2-EOS adapter (they are all ~11mm thick), so it occured to me it should be possible to modify one of my existing low profile
M42-EOS adapters, by replacing the yellow part with T2 insert from thick adapter.
I need to machine the black insert to mach the yellow insert dimensions.
Will post the result of this operation when I am done.
EDIT:
Another possibility is
this adapter... It is not as thin but it may be worth trying.