Stabilator – control horns problem (maybe)

I come across a weird thing.
I’ve put together the spar box assembly and tried on the control horns. (Page 09-03). They turned out to be about 1.5mm larger than the spar box. (see the attached pics). There must be some spacer or a doubler between the horns and the spar, but there is nothing in the plans.

Update:

Good people form VAF forum suggested fabricating and installing shim plates. It looks like this is a common issue.

http://www.vansairforce.com/community/showthread.php?t=122231

Here is a pic from one of the builders: