Misalignments caused by changed steel upright joining channel

The interior dimension of the upright joining channel CF-CHL-008-X-A-1 as supplied is about 129.5mm. According to to Sling this is right on the designed value. However examination of another aircraft has shown this dimension to be closer to 128.0mm. Seemingly the specification of this particular part has been changed. I attempted to spread the mismatch evenly by shifting rib 5 and the skin relative to this channel, with the idea of upsizing to 4.8mm rivers, however has advised that the skin and external reinforcing rib CF-RIB-005 must be referenced to the front seat mount angles CF-ANG-007 and the main spar carry-through angles. The consequence of this is the alignment of the skin and rib 5 holes at the rear seat mount angle CF-ANG-006 is thrown off. There is a mismatch of about 0.8mm on the RHS and less on the LHS between the skin/rib5 and the middle holes of th The mismatch between angle and the skin is about 1mm and the mismatch between the angle and the rib 5 holes is nearly 2mm. This is too large a mismatch to correct by upsizing to 4.8mm rivets. Sling have recommended replacement of the CF-ANG-006 and the rib 5 with custom variants with a number of hole omitted, which I can match drill.