I'm not sure how any of this is helping the poster. As I understand it, there is only space for a 2 cm coupling, and there is a problem with the drilled hole for the motor end of it. If I have read this correctly, you are trying to get that end straight and in line using grub screws. I don't think you have much chance. I would start with a new coupling, with the correct bores that are a tight fit on the shafts. Have a look at the couplings Dave Millbourn uses in his models, they can be bought an short lengths, use a good solid rubber insert and are proven.
I'm presuming that the 2 cm mentioned is the gap between motor shaft and the prop shaft, if so, you will also need to measure the total gap between motor end and the prop tube to find out the length of coupling that will fit in.
Lastly, on couplings in general, dog bone couplings are available in the uk, shg models sell them.
Chas