We had a kitchen extension many years ago - and now we’ve widened the opening flush to the walls, steels are in. ( sort of ) and now I need to tooth in the extension to main house. On removing the nib it became obvious the cavity on the extension is different. Measures 90mm - main house is 75. And the main house has been built a little on the **** so the blocks are actually out of line by about 40mm. Now…I could join and then batton out the wider side before plastering…but….I have to sit a padstone 575x215 where I’m toothing in. Any thoughts?