The difference is not too small, 3-4mm I measure:-
It was difficult and required a lot of patience.
This is close to done, but I would leave it alone first after like 2 hours of hard work:
When this is done, I've to enlarge the mount holes to fix it on the Mark-X mounting holes. And then I will need to drill two holes on the mounting plate to fix the DEC slow motion control worm block.