Hi Alberto.
An adapter plate is the way to go. I made one so I could fit a 160mm 3 jaw lathe chuck to a 150mm Vertex rotary table. It also allows for me to fit my 4 Jaw if needed.
I turned a plate from a piece of 20mm aluminium. From memory it was a grade that has properties similar to mild steel but easier to work and lighter.
The chuck mounting face is turned with a small lip to locate the chuck. This plate takes the place of the chuck back plate.
Special T nuts are made to fit the RT slots and extend up into the adapter plate.
Grub screws are screwed through the side of the plate and into holes in the T nuts. The grub screws have their ends tapered so that as they are tightened, they pull up on the T nuts, thus securing the plate against the RT.
I also turned a shaft with a 2MT to fit the centre of the RT. Clamp this lightly in the 3 jaw while tightening everything up and it is almost perfectly aligned.
Hope this all makes sense.