Does anybody know how to id a demon carb according to the pn on box it is a 750 dp but it has vacum sec looked all over it and cannot find any numbers also have a pair of thorley headers eo#d540 in a 65 coronet dont work with a 383/400 deck hight hit on steering linkage put in a 440 still hitting best I can figure they are for a 440 deck with indy heads looked in headers by dougs as well as thorley headers cannot locate them. Thank you for your help.