can anyone confirm what size thread is on the wilwood brake m/c threaded rod, the part the pedal pushes? I think its 3/8 unf?

think they are 5/16'' UNF you can confirm all these types of detail on the Willwood website - I would check there too.

same as these
http://www.cbsonline.co.uk/0625-master-cylinder-with-resevoir-ma625i-115-p.asp

5/16" unf is correct

Yes, 5/16 unf

Rally design sell the clevis to match
http://www.rallydesign.co.uk/product_info.php?cPath=562_582_587&products_id=4066