I've got a big RS500 cooler and it's mm's from the headlamp but it all fits nice.

Are you sure they are Cosworth headlamps and not std sapphire ones as the brackets are different? Might be your problem

http://ebayapi.loc8apartltd.netdna-cdn.com/00/s/NTQwWDk2MA==/z/WvQAAOSwk1JWhFoq/$_1.JPG

Cosworth ^^^

http://ebayapi.loc8apartltd.netdna-cdn.com/00/s/OTYwWDEyODA=/z/FOMAAOSwk1JWgGCA/$_1.JPG

standard ^^^