I often forget ! Try Josh Bennett, Miniimports. Let him know the issue you are having, he'll go through the new arms he has to be sure he's sending a good set. He's a great bloke and a very reputable supplier.
Isn't it a 1 in 8 taper? Annoying if the producerer didn't appreciate what that means for manufacturing tolerances.
It looks like there could be a mismatch on the maths too, could they be 1 in 10 taper as well???
I suppose they could be plugged & redrilled, but I'd be embarrassed to be the supplier if it came to that.
British stuff tends to be 7:1 (or 70 25') and American is 10:1 (or 90 30'). Machining tapers accurately requires a good deal of care, an 'opps' of going even as little as 5 thou too deep can be the difference between something usable and scrap.